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High-Frequency Mechanostimulation of Cell Adhesion
L.F. Kadem, K.G. Suana, M. Holz, W. Wang, H. Westerhaus, R. Herges and C. Selhuber-Unkel, Angewandte Chemie International Edition 2017, 56, 225-229.
Abstract:
Cell adhesion is regulated by molecularly defined protein interactions and by mechanical forces, which can activate a dynamic restructuring of adhesion sites. Previous attempts to explore the response of cell adhesion to forces have been limited to applying mechanical stimuli that involve the cytoskeleton. In contrast, we here apply a new, oscillatory type of stimulus through push–pull azobenzenes. Push–pull azobenzenes perform a high-frequency, molecular oscillation upon irradiation with visible light that has frequently been applied in polymer surface relief grating. We here use these oscillations to address single adhesion receptors. The effect of molecular oscillatory forces on cell adhesion has been analyzed using single-cell force spectroscopy and gene expression studies. Our experiments demonstrate a reinforcement of cell adhesion as well as upregulated expression levels of adhesion-associated genes as a result of the nanoscale “tickling” of integrins. This novel type of mechanical stimulus provides a previously unprecedented molecular control of cellular mechanosensing.
BibTeX:
@article{Kadem2017,
author = {Kadem, Laith F and Suana, K Grace and Holz, Michelle and Wang, Wei and Westerhaus, Hannes and Herges, Rainer and Selhuber-Unkel, Christine},
title = {High-Frequency Mechanostimulation of Cell Adhesion},
journal = {Angewandte Chemie International Edition},
publisher = {Wiley Online Library},
year = {2017},
volume = {56},
number = {1},
pages = {225-229},
doi = {http://doi.org/10.1002/anie.201609483}
}
Imine-Functionalized Triazatriangulenium Platforms: Towards an Artificial Ciliated Epithelium
M. Hammerich, T. Rusch, N.R. Krekiehn, A. Bloedorn, O.M. Magnussen and R. Herges, ChemPhysChem 2016, 17, 1870-1874.
Abstract:
Triazatriangulenium (TATA) platforms have been used to prepare highly ordered, self-assembled monolayers of free- and vertically standing imines on Au(111) surfaces. Upon irradiation, the imines undergo trans–cis isomerization and a fast thermal reaction (t1/2=0.58 s at 20 °C) back to the more stable trans form. It is known that the photochemical reaction proceeds through rotation of the C=N bond and the thermochemical reaction through inversion at the N atom. The imine motors, therefore, should be able to induce a net displacement of particles above the surface similar to cilia epithelia in nature.
BibTeX:
@article{Hammerich2016,
author = {Melanie Hammerich and Talina Rusch and Nicolai R. Krekiehn and Andreas Bloedorn and Olaf M. Magnussen and Rainer Herges},
title = {Imine-Functionalized Triazatriangulenium Platforms: Towards an Artificial Ciliated Epithelium},
journal = {ChemPhysChem},
publisher = {Wiley-Blackwell},
year = {2016},
volume = {17},
number = {12},
pages = {1870--1874},
doi = {http://doi.org/10.1002/cphc.201600147}
}
Heterodiazocines: Synthesis and Photochromic Properties, Trans to Cis Switching within the Bio-optical Window
M. Hammerich, C. Schütt, C. Stähler, P. Lentes, F. Röhricht, R. Höppner and R. Herges, Journal of the American Chemical Society 2016, 138, 13111-13114.
Abstract:
Diazocines, bridged azobenzenes, exhibit superior photophysical properties compared to parent azobenzenes such as high switching efficiencies, quantum yields, and particularly switching wavelengths in the visible range. Synthesis, however, proceeds with low yields, and derivatives are difficult to prepare. We now present two heterodiazocines which are easier to synthesize, and the general procedures should also provide facile access to derivatives. Moreover, both compounds can be switched with light in the far-red (650 nm). Accessibility and photophysical properties make them ideal candidates for applications such as photoswitchable drugs and functional materials.
BibTeX:
@article{Hammerich2016a,
author = {Hammerich, Melanie and Schütt, Christian and Stähler, Cosima and Lentes, Pascal and Röhricht, Fynn and Höppner, Ronja and Herges, Rainer},
title = {Heterodiazocines: Synthesis and Photochromic Properties, Trans to Cis Switching within the Bio-optical Window},
journal = {Journal of the American Chemical Society},
publisher = {ACS Publications},
year = {2016},
volume = {138},
number = {40},
pages = {13111--13114},
doi = {http://doi.org/10.1021/jacs.6b05846}
}
Azoimidazole functionalized Ni-porphyrins for molecular spin switching and light responsive MRI contrast agents
G. Heitmann, C. Schütt, J. Gröbner, L. Huber and R. Herges, Dalton Trans. 2016, 45, 11407-11412.
Abstract:
Azo-N-methylimidazole functionalized Ni(II)porphyrins were rationally designed and synthesized and their performance as molecular spin switches was investigated. They perform intramolecular light-driven coordination-induced spin state switching (LD-CISSS) in the presence of water and therefore are an important step towards spin switches for medicinal applications, particularly functional MRI contrast agents.
BibTeX:
@article{Heitmann2016,
author = {Gernot Heitmann and Christian Schütt and Jens Gröbner and Lukas Huber and Rainer Herges},
title = {Azoimidazole functionalized Ni-porphyrins for molecular spin switching and light responsive MRI contrast agents},
journal = {Dalton Trans.},
publisher = {Royal Society of Chemistry (RSC)},
year = {2016},
volume = {45},
number = {28},
pages = {11407--11412},
doi = {http://doi.org/10.1039/c6dt01727d}
}
Spin State Switching in Solution with an Azoimidazole-Functionalized Nickel(II)-Porphyrin
G. Heitmann, C. Schütt and R. Herges, European Journal of Organic Chemistry 2016, 2016, 3817-3823.
Abstract:
We herein report the synthesis and switching properties of an azo-1-methylimidazole-functionalized Ni2+ porphyrin. Upon irradiation and cis/trans isomerization of the azo unit, 1-methylimidazole is reversibly coordinated as an axial ligand to the Ni2+ porphyrin. Consequently, the Ni2+ is switched between a diamagnetic low-spin state (trans) and a paramagnetic high-spin state (cis) according to the light-driven coordination-induced spin state switching (LD-CISSS) principle. The spin state switching is operable in solution under ambient conditions. The paramagnetic cis-species is formed in exceptionally high amounts upon irradiation with UV light (365 nm), whereas an excess of the diamagnetic trans-species was obtained upon irradiation with blue light (430 nm).
BibTeX:
@article{Heitmann2016a,
author = {Gernot Heitmann and Christian Schütt and Rainer Herges},
title = {Spin State Switching in Solution with an Azoimidazole-Functionalized Nickel(II)-Porphyrin},
journal = {European Journal of Organic Chemistry},
publisher = {Wiley-Blackwell},
year = {2016},
volume = {2016},
number = {22},
pages = {3817--3823},
doi = {http://doi.org/10.1002/ejoc.201600548}
}
Modular Synthetic Route to Monofunctionalized Porphyrin Architectures
G. Heitmann, M. Dommaschk, R. Löw and R. Herges, Organic Letters 2016, 18, 5228-5231.
Abstract:
The synthesis of a borylated Ni2+ porphyrin and its application as a versatile precursor for building up functional ortho-substituted tetraaryl porphyrin architectures is reported. This precursor porphyrin provides the basis for efficient modular syntheses of porphyrin compounds with covalently attached axial ligands which are important as enzyme model complexes, electron transfer dyads, and many other applications. In the present study, the precursor porphyrin was used for the synthesis of molecular spin switches which previously showed high potential as photoresponsive contrast agents for magnetic resonance imaging.
BibTeX:
@article{Heitmann2016b,
author = {Heitmann, Gernot and Dommaschk, Marcel and Löw, Roland and Herges, Rainer},
title = {Modular Synthetic Route to Monofunctionalized Porphyrin Architectures},
journal = {Organic Letters},
publisher = {ACS Publications},
year = {2016},
volume = {18},
number = {20},
pages = {5228--5231},
doi = {http://doi.org/10.1021/acs.orglett.6b02507}
}
Indacenodibenzothiophenes: synthesis, optoelectronic properties and materials applications of molecules with strong antiaromatic character
J.L. Marshall, K. Uchida, C.K. Frederickson, C. Schütt, A.M. Zeidell, K.P. Goetz, T.W. Finn, K. Jarolimek, L.N. Zakharov, C. Risko, R. Herges, O.D. Jurchescu and M.M. Haley, Chem. Sci. 2016, 7, 5547-5558.
Abstract:
Indeno[1,2-b]fluorenes (IFs), while containing 4n π-electrons, are best described as two aromatic benzene rings fused to a weakly paratropic s-indacene core. In this study, we find that replacement of the outer benzene rings of an IF with benzothiophenes allows the antiaromaticity of the central s-indacene to strongly reassert itself. Herein we report a combined synthetic, computational, structural, and materials study of anti- and syn-indacenodibenzothiophenes (IDBTs). We have developed an efficient and scalable synthesis for preparation of a series of aryl- and ethynyl-substituted IDBTs. NICS-XY scans and ACID calculations reveal an increasingly antiaromatic core from [1,2-b]IF to anti-IDBT, with syn-IDBT being nearly as antiaromatic as the parent s-indacene. As an initial evaluation, the intermolecular electronic couplings and electronic band structure of a diethynyl anti-IDBT derivative reveal the potential for hole and/or electron transport. OFETs constructed using this molecule show the highest hole mobilities yet achieved for a fully conjugated IF derivative.
BibTeX:
@article{Marshall2016,
author = {Jonathan L. Marshall and Kazuyuki Uchida and Conerd K. Frederickson and Christian Schütt and Andrew M. Zeidell and Katelyn P. Goetz and Tristan W. Finn and Karol Jarolimek and Lev N. Zakharov and Chad Risko and Rainer Herges and Oana D. Jurchescu and Michael M. Haley},
title = {Indacenodibenzothiophenes: synthesis, optoelectronic properties and materials applications of molecules with strong antiaromatic character},
journal = {Chem. Sci.},
publisher = {Royal Society of Chemistry (RSC)},
year = {2016},
volume = {7},
number = {8},
pages = {5547--5558},
doi = {http://doi.org/10.1039/c6sc00950f}
}
Design and Synthesis of Photodissociable Ligands Based on Azoimidazoles for Light-Driven Coordination-Induced Spin State Switching in Homogeneous Solution
C. Schütt, G. Heitmann, T. Wendler, B. Krahwinkel and R. Herges, The Journal of Organic Chemistry 2016, 81, 1206-1215.
Abstract:
Light-switchable azoimidazoles were rationally designed and synthesized, and their performance was investigated as photodissociable ligands (PDL) and for spin state switching of Ni porphyrins. The rationally designed ligands exhibit a high photochemical conversion rate (trans → cis > 98%) and no measurable fatigue over a large number of switching cycles at room temperature under air. As compared to the known phenylazopyridines, the phenylazoimidazoles exhibit a much stronger affinity as axial ligands to Ni porphyrin in the binding trans configuration and a low affinity in their cis form. This affinity switching was used to control the coordination number of Ni2+. Concomitant with the change in coordination number is the change of the spin state from triplet (high spin) to singlet state (low spin). We report on phenylazoimidazole-based PDLs that switch the paramagnetic ratio of the investigated nickel species by up to 70%. Consequently, azoimidazoles exhibit considerably higher switching efficiencies than previously described pyridine-based PDLs.
BibTeX:
@article{Schuett2016,
author = {Christian Schütt and Gernot Heitmann and Thore Wendler and Bahne Krahwinkel and Rainer Herges},
title = {Design and Synthesis of Photodissociable Ligands Based on Azoimidazoles for Light-Driven Coordination-Induced Spin State Switching in Homogeneous Solution},
journal = {The Journal of Organic Chemistry},
publisher = {American Chemical Society (ACS)},
year = {2016},
volume = {81},
number = {3},
pages = {1206--1215},
doi = {http://doi.org/10.1021/acs.joc.5b02817}
}
Photoswitchable Magnetic Resonance Imaging Contrast by Improved Light-Driven Coordination-Induced Spin State Switch
M. Dommaschk, M. Peters, F. Gutzeit, C. Schütt, C. Näther, F.D. Sönnichsen, S. Tiwari, C. Riedel, S. Boretius and R. Herges, J. Am. Chem. Soc. 2015, 137, 7552-7555.
Abstract:
We present a fully reversible and highly efficient on–off photoswitching of magnetic resonance imaging (MRI) contrast with green (500 nm) and violet-blue (435 nm) light. The contrast change is based on intramolecular light-driven coordination-induced spin state switch (LD-CISSS), performed with azopyridine-substituted Ni-porphyrins. The relaxation time of the solvent protons in 3 mM solutions of the azoporphyrins in DMSO was switched between 3.5 and 1.7 s. The relaxivity of the contrast agent changes by a factor of 6.7. No fatigue or side reaction was observed, even after >100 000 switching cycles in air at room temperature. Electron-donating substituents at the pyridine improve the LD-CISSS in two ways: better photostationary states are achieved, and intramolecular binding is enhanced.
BibTeX:
@article{Dommaschk2015,
author = {Marcel Dommaschk and Morten Peters and Florian Gutzeit and Christian Schütt and Christian Näther and Frank D. Sönnichsen and Sanjay Tiwari and Christian Riedel and Susann Boretius and Rainer Herges},
title = {Photoswitchable Magnetic Resonance Imaging Contrast by Improved Light-Driven Coordination-Induced Spin State Switch},
journal = {J. Am. Chem. Soc.},
publisher = {American Chemical Society (ACS)},
year = {2015},
volume = {137},
number = {24},
pages = {7552--7555},
doi = {http://doi.org/10.1021/jacs.5b00929}
}
Coordination-Induced Spin-State Switching with Nickel Chlorin and Nickel Isobacteriochlorin
M. Dommaschk, V. Thoms, C. Schütt, C. Näther, R. Puttreddy, K. Rissanen and R. Herges, Inorganic Chemistry 2015, 54, 9390-9392.
Abstract:
We present the first coordination-induced spin-state switching with nickel chlorin and nickel isobacteriochlorin. The spin-state switching was monitored by UV–vis spectroscopy and NMR titration experiments. The association constants (K1 and K2) and thermodynamic parameters (ΔH and ΔS) of the coordination of pyridine were determined. The first X-ray analyses of a paramagnetic nickel chlorin and a nickel isobacteriochlorin provide further information about the structure of the octahedral complexes. Nickel chlorin and even more pronounced nickel isobacteriochlorin exhibit stronger coordination of axial ligands compared to the corresponding nickel porphyrin and thus provide the basis for more efficient spin-switching systems.
BibTeX:
@article{Dommaschk2015a,
author = {Marcel Dommaschk and Vanessa Thoms and Christian Schütt and Christian Näther and Rakesh Puttreddy and Kari Rissanen and Rainer Herges},
title = {Coordination-Induced Spin-State Switching with Nickel Chlorin and Nickel Isobacteriochlorin},
journal = {Inorganic Chemistry},
publisher = {American Chemical Society (ACS)},
year = {2015},
volume = {54},
number = {19},
pages = {9390--9392},
doi = {http://doi.org/10.1021/acs.inorgchem.5b01756}
}
Synthesis of Functionalized Perfluorinated Porphyrins for Improved Spin Switching
M. Dommaschk, C. Näther and R. Herges, The Journal of Organic Chemistry 2015, 80, 8496-8500.
Abstract:
We have established a method to synthesize perfluorinated meso-phenylporphyrins with one phenyl group bearing a substituent in the ortho position. These novel electron-deficient porphyrins are interesting for model enzymes, catalysis, photodynamic therapy, and electron transfer. The key step is the synthesis of an iodine-substituted porphyrin and its Suzuki cross coupling with boronic acid derivatives. We applied the novel strategy to synthesize a highly electron-deficient, azopyridine-substituted Ni–porphyrin that undergoes an improved ligand-driven coordination-induced spin-state switch.
BibTeX:
@article{Dommaschk2015b,
author = {M. Dommaschk and C. Näther and R. Herges},
title = {Synthesis of Functionalized Perfluorinated Porphyrins for Improved Spin Switching},
journal = {The Journal of Organic Chemistry},
publisher = {American Chemical Society (ACS)},
year = {2015},
volume = {80},
number = {17},
pages = {8496--8500},
doi = {http://doi.org/10.1021/acs.joc.5b01524}
}
Laterally Mounted Azobenzenes on Platforms
M. Hammerich and R. Herges, The Journal of Organic Chemistry 2015, 80, 11233-11236.
Abstract:
Triazatriangulenium ions have previously been used as platforms to prepare self-assembled monolayers of functional molecules such as azobenzenes with vertical orientation and that are free-standing on gold surfaces. We have now prepared azobenzenes that are spanned between two posts which are attached on two platforms. Absorbed on a gold surface, the azobenzene should be laterally oriented at a distance of more than 4 Å above and thus electronically decoupled from the surface, and the system should perform a muscle-type movement upon isomerization
BibTeX:
@article{Hammerich2015,
author = {Melanie Hammerich and Rainer Herges},
title = {Laterally Mounted Azobenzenes on Platforms},
journal = {The Journal of Organic Chemistry},
publisher = {American Chemical Society (ACS)},
year = {2015},
volume = {80},
number = {22},
pages = {11233--11236},
doi = {http://doi.org/10.1021/acs.joc.5b02262}
}
High-conductance surface-anchoring of a mechanically flexible platform-based porphyrin complex
N. Hauptmann, L. Groß, K. Buchmann, K. Scheil, C. Schütt, F.L. Otte, R. Herges, C. Herrmann and R. Berndt, New Journal of Physics 2015, 17, 013012.
Abstract:
The conductances of molecular model junctions comprising a triazatriangulenium platform with or without an ethynyl spacer and an upright Zn-porphyrin are probed with a low-temperature scanning probe microscope. The platform alone is found to be highly conductive. The ethynyl-linked Zn-porphyrin moiety reduces the conductance by three orders of magnitude and leads to an unexpected, non-monotonous variation of the force that was measured simultaneously at the tip of the microscope. Density functional theory calculations show that this variation results from an induced tilting of the porphyrin.
BibTeX:
@article{Hauptmann2015,
author = {Nadine Hauptmann and Lynn Groß and Kristof Buchmann and Katharina Scheil and Christian Schütt and Franziska L Otte and Rainer Herges and Carmen Herrmann and Richard Berndt},
title = {High-conductance surface-anchoring of a mechanically flexible platform-based porphyrin complex},
journal = {New Journal of Physics},
publisher = {IOP Publishing},
year = {2015},
volume = {17},
number = {1},
pages = {013012},
doi = {http://doi.org/10.1088/1367-2630/17/1/013012}
}
Coarctate and Pseudocoarctate Reactions: Stereochemical Rules
R. Herges, The Journal of Organic Chemistry 2015, 80, 11869-11876.
Abstract:
Coarctate reactions are a distinct class of concerted reactions. They differ from other concerted reactions, such as SN2, E2, or pericyclic reactions, in such a way that atoms are involved in the transition state at which two bonds are made and two bonds are broken simultaneously. Similar to pericyclic reactions, an electron count can be used to predict reactivity and stereochemistry. The “coarctate rules” are derived from a topological variant of the aromaticity of the transition state principle. Pseudocoarctate transition states exhibit disconnections in the topology of orbital overlap and do not necessarily follow the coarctate rules.
BibTeX:
@article{Herges2015,
author = {Rainer Herges},
title = {Coarctate and Pseudocoarctate Reactions: Stereochemical Rules},
journal = {The Journal of Organic Chemistry},
publisher = {American Chemical Society (ACS)},
year = {2015},
volume = {80},
number = {23},
pages = {11869--11876},
doi = {http://doi.org/10.1021/acs.joc.5b01959}
}
Rapid Reversible Photoswitching of Integrin-Mediated Adhesion at the Single-Cell Level
L.F. Kadem, M. Holz, K.G. Suana, Q. Li, C. Lamprecht, R. Herges and C. Selhuber-Unkel, Adv. Mater. 2015, 28, 1799-1802.
Abstract:
Rapid and reversible photoswitching of cell adhesion is achieved by c(RGDfK)-azobenzenes embedded in a poly(ethylene glycol) background on surfaces. The light-induced cis–trans-isomerization of the azobenzene enables switching of cell adhesion on the surface. Reversibility of switching over several consecutive switching cycles is demonstrated by single-cell force spectroscopy.
BibTeX:
@article{Kadem2015,
author = {Laith F. Kadem and Michelle Holz and Kristine Grace Suana and Qian Li and Constanze Lamprecht and Rainer Herges and Christine Selhuber-Unkel},
title = {Rapid Reversible Photoswitching of Integrin-Mediated Adhesion at the Single-Cell Level},
journal = {Adv. Mater.},
publisher = {Wiley-Blackwell},
year = {2015},
volume = {28},
number = {9},
pages = {1799--1802},
doi = {http://doi.org/10.1002/adma.201504394}
}
UV/Vis Spectroscopy Studies of the Photoisomerization Kinetics in Self-Assembled Azobenzene-Containing Adlayers
N.R. Krekiehn, M. Müller, U. Jung, S. Ulrich, R. Herges and O.M. Magnussen, Langmuir 2015, 31, 8362-8370.
Abstract:
Direct comparative studies of the photoisomerization of azobenzene derivatives in self-assembled adlayers on Au and as free molecules in dichloromethane solution were performed using UV/vis spectroscopy. For all studied systems a highly reversible trans–cis isomerization in the adlayer is observed. Quantitative studies of the absorbance changes and photoisomerization kinetics reveal that in azobenzenes mounted as freestanding vertical groups on the surface via triazatriangulene-based molecular platforms photoswitching is nearly uninhibited by the local environment in the adlayer. The blue-shift of the π–π* transition in adlayers of these molecules is in good agreement with theoretical studies of the effect of excitonic coupling between the molecules. In contrast, in azobenzene-containing thiol self-assembled monolayers the fraction of photoswitching molecules and the photoisomerization kinetics are significantly reduced compared to free molecules in solution.
BibTeX:
@article{Krekiehn2015,
author = {N. R. Krekiehn and M. Müller and U. Jung and S. Ulrich and R. Herges and O. M. Magnussen},
title = {UV/Vis Spectroscopy Studies of the Photoisomerization Kinetics in Self-Assembled Azobenzene-Containing Adlayers},
journal = {Langmuir},
publisher = {American Chemical Society (ACS)},
year = {2015},
volume = {31},
number = {30},
pages = {8362--8370},
doi = {http://doi.org/10.1021/acs.langmuir.5b01645}
}
Triazatriangulenium adlayers on Au(111): Superstructure as a function of alkyl side chain length
S. Lemke, S. Ulrich, F. Claußen, A. Bloedorn, U. Jung, R. Herges and O.M. Magnussen, Surface Science 2015, 632, 71-76.
Abstract:
The structure of organic adlayers, formed by self-assembly of molecular platforms of triazatriangulenium ions on Au(111), was systematically studied by scanning tunneling microscopy as a function of the length of the lateral ligands for alkyl side chains from propyl to dodecyl. A series of hexagonally-ordered adlayers with spacings from 10.7 Å (propyl) to 13.6 Å (dodecyl) was found which are commensurate to the Au(111) substrate lattice, indicating localized bonding of the molecules to the metal.
BibTeX:
@article{Lemke2014,
author = {Lemke, Sonja and Ulrich, Sandra and Claußen, Frauke and Bloedorn, Andreas and Jung, Ulrich and Herges, Rainer and Magnussen, Olaf M.},
title = {Triazatriangulenium adlayers on Au(111): Superstructure as a function of alkyl side chain length},
journal = {Surface Science},
publisher = {Elsevier BV},
year = {2015},
volume = {632},
pages = {71-76},
doi = {http://doi.org/10.1016/j.susc.2014.08.028}
}
X-ray spectroscopy characterization of azobenzene-functionalized triazatriangulenium adlayers on Au(111) surfaces
S. Ulrich, U. Jung, T. Strunskus, C. Schütt, A. Bloedorn, S. Lemke, E. Ludwig, L. Kipp, F. Faupel, O. Magnussen and R. Herges, Phys. Chem. Chem. Phys. 2015, 17, 17053-17062.
Abstract:
Triazatriangulenium (TATA) platform molecules allow the preparation of functionalized surfaces with well-defined lateral spacings of freestanding functional groups. Using scanning tunneling microscopy, synchrotron-based X-ray photoelectron spectroscopy, near edge X-ray absorption fine structure spectroscopy and complementary density functional theory calculations the chemical composition and orientational order of adlayers of functionalized azobenzene containing TATA platform molecules were characterized. According to these studies the molecules are chemically intact on the surface after self-assembly from solution and exhibit a well-defined adsorption geometry where the azobenzene units are oriented almost perpendicular to the surface.
BibTeX:
@article{Ulrich2015,
author = {Sandra Ulrich and Ulrich Jung and Thomas Strunskus and Christian Schütt and Andreas Bloedorn and Sonja Lemke and Eric Ludwig and Lutz Kipp and Franz Faupel and Olaf Magnussen and Rainer Herges},
title = {X-ray spectroscopy characterization of azobenzene-functionalized triazatriangulenium adlayers on Au(111) surfaces},
journal = {Phys. Chem. Chem. Phys.},
publisher = {Royal Society of Chemistry (RSC)},
year = {2015},
volume = {17},
number = {26},
pages = {17053--17062},
doi = {http://doi.org/10.1039/c5cp01447f}
}
Photoswitching in nanoporous, crystalline solids: an experimental and theoretical study for azobenzene linkers incorporated in MOFs
Z. Wang, L. Heinke, J. Jelic, M. Cakici, M. Dommaschk, R.J. Maurer, H. Oberhofer, S. Grosjean, R. Herges, S. Bräse, K. Reuter and C. Wöll, Phys. Chem. Chem. Phys. 2015, 17, 14582-14587.
Abstract:
In this article, we use the popular photoswitchable molecule, azobenzene, to demonstrate that the embedding in a nanoporous, crystalline solid enables a precise understanding of light-induced, reversible molecular motion. We investigate two similar azobenzene-containing, pillared-layer metal–organic frameworks (MOFs): Cu2(AzoBPDC)2(BiPy) and Cu2(NDC)2(AzoBiPy). Experimental results from UV-vis spectroscopy and molecular uptake experiments as well as theoretical results based on density-functional theory (DFT) show that in the Cu2(AzoBPDC)2(BiPy) MOF structure, the azobenzene side groups undergo photoisomerization when irradiated with UV or visible light. In a very similar MOF structure, Cu2(NDC)2(AzoBiPy), the experimental studies show an unexpected absence of photoisomerization. The DFT calculations reveal that in both MOFs the initial and final states of the photoswitching process (the trans and the cis conformation) have similar energies, which strongly suggests that the reason for the effective blocking of photoswitching in the AzoBiPy-based MOFs must be related to the switching process itself. More detailed calculations show that in Cu2(NDC)2(AzoBiPy) a naphthalene linker from the molecular framework blocks the photoisomerization trajectory which leads from the trans to the cis conformation. For Cu2(AzoBPDC)2(BiPy), as a result of the different geometry, such a steric hindrance is absent.
BibTeX:
@article{Wang2015,
author = {Zhengbang Wang and Lars Heinke and Jelena Jelic and Murat Cakici and Marcel Dommaschk and Reinhard J. Maurer and Harald Oberhofer and Sylvain Grosjean and Rainer Herges and Stefan Bräse and Karsten Reuter and Christof Wöll},
title = {Photoswitching in nanoporous, crystalline solids: an experimental and theoretical study for azobenzene linkers incorporated in MOFs},
journal = {Phys. Chem. Chem. Phys.},
publisher = {Royal Society of Chemistry (RSC)},
year = {2015},
volume = {17},
number = {22},
pages = {14582--14587},
doi = {http://doi.org/10.1039/c5cp01372k}
}
Aggregation-Induced-Emission-Active Macrocycle Exhibiting Analogous Triply and Singly Twisted Möbius Topologies
E. Wang, Z. He, E. Zhao, L. Meng, C. Schütt, J.W.Y. Lam, H.H.Y. Sung, I.D. Williams, X. Huang, R. Herges and B.Z. Tang, Chemistry - A European Journal 2015, 21, 11707-11711.
Abstract:
Molecules with Möbius topology have drawn increasing attention from scientists in a variety of fields, such as organic chemistry, inorganic chemistry, and material science. However, synthetic difficulties and the lack of functionality impede their fundamental understanding and practical applications. Here, we report the facile synthesis of an aggregation-induced-emission (AIE)-active macrocycle (TPE-ET) and investigate its analogous triply and singly twisted Möbius topologies. Because of the twisted and flexible nature of the tetraphenylethene units, the macrocycle adjusts its conformations so as to accommodate different guest molecules in its crystals. Moreover, theoretical studies including topological and electronic calculations reveal the energetically favorable interconversion process between triply and singly twisted topologies.
BibTeX:
@article{Wang2015a,
author = {Erjing Wang and Zikai He and Engui Zhao and Luming Meng and Christian Schütt and Jacky W. Y. Lam and Herman H. Y. Sung and Ian D. Williams and Xuhui Huang and Rainer Herges and Ben Zhong Tang},
title = {Aggregation-Induced-Emission-Active Macrocycle Exhibiting Analogous Triply and Singly Twisted Möbius Topologies},
journal = {Chemistry - A European Journal},
publisher = {Wiley-Blackwell},
year = {2015},
volume = {21},
number = {33},
pages = {11707--11711},
doi = {http://doi.org/10.1002/chem.201502224}
}
Coordination-Induced Spin-State-Switch (CISSS) in water
M. Dommaschk, F. Gutzeit, S. Boretius, R. Haag and R. Herges, Chem. Commun. 2014, 50, 12476-12478.
Abstract:
We present a non-ionic water-soluble porphyrin that does not exhibit measurable aggregation even at high concentrations in water. The spin state of the corresponding nickel(II) complex changes from completely diamagnetic (low-spin) to paramagnetic (high-spin) upon addition of a strong axial ligand. This leads to a strongly reduced NMR relaxation time of the water protons even at low concentrations of the complex.
BibTeX:
@article{Dommaschk2014,
author = {Dommaschk, Marcel and Gutzeit, Florian and Boretius, Susann and Haag, Rainer and Herges, Rainer},
title = {Coordination-Induced Spin-State-Switch (CISSS) in water},
journal = {Chem. Commun.},
year = {2014},
volume = {50},
pages = {12476-12478},
doi = {http://doi.org/10.1039/c4cc05525j}
}
Rational Design of a Room Temperature Molecular Spin Switch. The Light-Driven Coordination Induced Spin State Switch (LD-CISSS) Approach.
M. Dommaschk, C. Schutt, S. Venkataramani, U. Jana, C. Nather, F.D. Soennichsen and R. Herges, Dalton Trans. 2014, published online.
Abstract:
Extensive use of quantum chemical calculations has been made to rationally design a molecule whose spin state can be switched reversibly using light of two different wavelengths at room temperature in solution. Spin change is induced by changing the coordination number of a nickel complex. The coordination number in turn is switched using a photochromic ligand that binds in one configuration and dissociates in the other. We demonstrate that successful design relies on a precise geometry fit and delicate electronic tuning. Our designer complex exhibits an extremely high long-term switching stability (more than 20,000 cycles) and a high switching efficiency. The high-spin state is extraordinarily stable with a half-life of 400 days at room temperature. Switching between the dia- and paramagnetic state is achieved with visible light (500 and 430 nm). The compound can also be used as a molecular logic gate with light and pH as input and the magnetic state as non-destructive read-out.
BibTeX:
@article{Dommaschk2014a,
author = {Dommaschk, Marcel and Schutt, Christian and Venkataramani, Sugumar and Jana, Umasish and Nather, Christian and Soennichsen, Frank D and Herges, Rainer},
title = {Rational Design of a Room Temperature Molecular Spin Switch. The Light-Driven Coordination Induced Spin State Switch (LD-CISSS) Approach.},
journal = {Dalton Trans.},
year = {2014},
pages = {published online},
doi = {http://doi.org/10.1039/C4DT03048F}
}
Photoswitching in Two-Component Surface-Mounted Metal-Organic Frameworks: Optically Triggered Release from a Molecular Container.
L. Heinke, M. Cakici, M. Dommaschk, S. Grosjean, R. Herges, S. Braese and C. Woell, ACS Nano 2014, 8, 1463-1467.
Abstract:
The remote control of surface properties is one of the key challenges in interfacial systems chem. The authors report the realization of a SURMOF (surface-mounted metal-org. framework)-based hybrid system in which a crucial component can be switched by light. The realization of this two-component system is made possible by installing vertical compositional gradients via liq.-phase epitaxy. After loading the porous coating with guest mols., its release is initiated by illumination with visible light and monitored by a quartz crystal microbalance.
BibTeX:
@article{Heinke2014,
author = {Heinke, Lars and Cakici, Murat and Dommaschk, Marcel and Grosjean, Sylvain and Herges, Rainer and Braese, Stefan and Woell, Christof.},
title = {Photoswitching in Two-Component Surface-Mounted Metal-Organic Frameworks: Optically Triggered Release from a Molecular Container.},
journal = {ACS Nano},
year = {2014},
volume = {8},
number = { },
pages = {1463-1467},
doi = {http://doi.org/10.1021/nn405469g}
}
A Shuttle for the Transport of Protons Based on a [2]Rotaxane.
B. Hesseler, M. Zindler, R. Herges and U. Luening, Eur. J. Org. Chem. 2014, 3885-3901.
Abstract:
A [2]rotaxane shuttle for (light-driven) proton transport has been designed and synthesized. The rotaxane contains a macrocyclic ring that carries a pyridine nitrogen atom as a basic center to bind and to transport a proton. The axis includes an amide binding site for the macrocycle and a pos. charge in close vicinity. Upon protonation of the pyridine nitrogen atom, the hydrogen bond is broken and Coulomb repulsion between the protonated pyridine and the permanent pos. charge in the axis pushes the protonated macrocycle to the other end of the axis. By variation of the pH the ring can shuttle to and fro. Its locations on the axis were detd. by NMR spectroscopy.
BibTeX:
@article{Hesseler2014,
author = {Hesseler, Britta and Zindler, Melanie and Herges, Rainer and Luening, Ulrich.},
title = {A Shuttle for the Transport of Protons Based on a [2]Rotaxane.},
journal = {Eur. J. Org. Chem.},
year = {2014},
number = { },
pages = {3885-3901},
doi = {http://doi.org/10.1002/ejoc.201402249}
}
Monitoring the reversible photoisomerization of an azobenzene-functionalized molecular triazatriangulene platform on Au(111) by IRRAS
H. Jacob, S. Ulrich, U. Jung, S. Lemke, T. Rusch, C. Schütt, F. Petersen, T. Strunskus, O. Magnussen, R. Herges and F. Tuczek, Phys. Chem. Chem. Phys. 2014, 16, 22643-22650.
Abstract:
Spectroscopic evidence of a reversible, photoinduced trans ↔ cis photoisomerization is provided for an azobenzene-functionalized triazatriangulene (TATA) platform on Au(111). As shown by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), these molecules form a well-ordered self-assembled monolayer (SAM) on Au(111). The surface-adsorbed azo-TATA platforms are also investigated by infrared reflection absorption spectroscopy (IRRAS); a methoxy marker group at the upper phenyl ring of the azo moiety is employed to monitor the switching state. The IRRAS data are analyzed by comparison with theoretical and transmission IR spectra as well as bulk and surface-enhanced Raman spectroscopic (SERS) data. IRRAS shows that the methoxy group is oriented perpendicular to the surface in trans- and tilted with respect to the surface normal in cis-configuration. This indicates that the photoswitching capability of the azobenzene moieties is retained on the gold surface. The lifetime of the cis-configuration is, however, reduced by a factor of 103 with respect to the homogeneous solution.
BibTeX:
@article{Jacob2014,
author = {Jacob, Hanne and Ulrich, Sandra and Jung, Ulrich and Lemke, Sonja and Rusch, Talina and Schütt, Christian and Petersen, Finn and Strunskus, Thomas and Magnussen, Olaf and Herges, Rainer and Tuczek, Felix},
title = {Monitoring the reversible photoisomerization of an azobenzene-functionalized molecular triazatriangulene platform on Au(111) by IRRAS},
journal = {Phys. Chem. Chem. Phys.},
year = {2014},
volume = {16},
pages = {22643-22650},
doi = {http://doi.org/10.1039/c4cp03438d}
}
Ordered Monolayers of Free-Standing Porphyrins on Gold
F.L. Otte, S. Lemke, C. Schütt, N.R. Krekiehn, U. Jung, O.M. Magnussen and R. Herges, Journal of the American Chemical Society 2014, 136, 11248-11251.
Abstract:
The controlled attachment of chromophores to metal or semiconducting surfaces is a prerequisite for the construction of photonic devices and artificial surface-based light-harvesting systems. We present an approach to mount porphyrins in ordered monolayers on Au(111) by self-assembly and verify it, employing STM, absorption spectroscopy, and quantum chemical calculations. The usual adsorption geometry of planar chromophores, flat on the surface or densely packed edge-on, is prevented by mounting the porphyrins upright on a molecular platform. An ethynyl unit as spacer and pivot joint provides almost free azimuthal rotation of the unsubstituted porphin. However, rotation of the larger triphenylporphyrin unit is sterically restricted: because the diameter of the substituted porphyrin is larger than the distance to its next neighbors, the phenyl substituents of neigboring molecules interact by dispersion force, which leads to an alignment of the azimuthal rotators.
BibTeX:
@article{Otte2014,
author = {Otte, Franziska L. and Lemke, Sonja and Schütt, Christian and Krekiehn, Nicolai R. and Jung, Ulrich and Magnussen, Olaf M. and Herges, Rainer},
title = {Ordered Monolayers of Free-Standing Porphyrins on Gold},
journal = {Journal of the American Chemical Society},
year = {2014},
volume = {136},
pages = {11248-11251},
doi = {http://doi.org/10.1021/ja505563e}
}
7-​Isopropylidene-​N2,​N3,​N5,​N6-​tetramethoxy-​N2,​N3,​N5,​N6-​tetramethylbicyclo[2.2.1]​hepta-​2,​5-​diene-​2,​3,​5,​6-​tetracarboxamide
B. Sahlmann, C. Näther and R. Herges, Acta Crystallographica Section E 2014, 70, o438.
Abstract:
Although the mol­ecular structure of the title compound, C22H32N4O8, displays a twofold symmetry of the mol­ecule including the meth­oxy and methyl substituents, no crystallographic twofold symmetry is observed in the X-ray structure analysis. The carbonyl O atoms alternately point to different sides of the plane defined by the carbonyl C atoms. Two meth­oxy groups are oriented inside the mol­ecules cavity. The H atoms of two methyl groups are disordered over two orientations and were refined using a split model.
BibTeX:
@article{Sahlmann2014,
author = {Sahlmann, Benjamin and Näther, Christian and Herges, Rainer},
title = {7-​Isopropylidene-​N2,​N3,​N5,​N6-​tetramethoxy-​N2,​N3,​N5,​N6-​tetramethylbicyclo[2.2.1]​hepta-​2,​5-​diene-​2,​3,​5,​6-​tetracarboxamide},
journal = {Acta Crystallographica Section E},
year = {2014},
volume = {70},
number = {4},
pages = {o438},
doi = {http://doi.org/10.1107/S1600536814004255}
}
Design and synthesis of the first triply twisted Mobius annulene.
G.R. Schaller, F. Topic, K. Rissanen, Y. Okamoto, J. Shen and R. Herges, Nat. Chem. 2014, 6, 608-613.
Abstract:
As long as 50 years ago theor. calcns. predicted that Mobius annulenes with only one π surface and one edge would exhibit peculiar electronic properties and violate the Huckel rules. Numerous synthetic attempts notwithstanding, the first singly twisted Mobius annulene was not prepd. until 2003. Here we present a general, rational strategy to synthesize triply or even more highly twisted cyclic π systems. We apply this strategy to the prepn. of a triply twisted [24]dehydroannulene, the structure of which was confirmed by X-ray anal. Our strategy is based on the topol. transformation of 'twist' into 'writhe'. The advantage is twofold: the product exhibits a lower degree of strain and precursors can be designed that inherently include the writhe, which, after cyclization, ends up in the Mobius product. With our strategy, triply twisted systems are easier to prep. than their singly twisted counterparts.
BibTeX:
@article{Schaller2014,
author = {Schaller, Gaston R. and Topic, Filip and Rissanen, Kari and Okamoto, Yoshio and Shen, Jun and Herges, Rainer.},
title = {Design and synthesis of the first triply twisted Mobius annulene.},
journal = {Nat. Chem.},
year = {2014},
volume = {6},
number = { },
pages = {608-613},
doi = {http://doi.org/10.1038/nchem.1955}
}
Schüler schalten chemisch.
S. Schwarzer, D. Ingwersen, R. Herges and I. Parchmann, Nachr. Chem. 2014, 62, 491-495.
Abstract:
Wenn chemische Grundlagenforschung und Fachdidaktik zusammenarbeiten, profitieren beide Seiten. Ein Beispiel ist der Sonderforschungsbereich “Funktion durch Schalten” an der Universität Kiel, dessen Ergebnisse und Arbeitsweisen nun in Chemieunterricht und Schülerlabor einfließen.
BibTeX:
@article{Schwarzer2014,
author = {Schwarzer, Stefan and Ingwersen, Daniela and Herges, Rainer and Parchmann, Ilka.},
title = {Schüler schalten chemisch.},
journal = {Nachr. Chem.},
year = {2014},
volume = {62},
number = { },
pages = {491-495},
doi = {http://doi.org/10.1002/nadc.201490145}
}
Diazocines on Molecular Platforms
T. Tellkamp, J. Shen, Y. Okamoto and R. Herges, European Journal of Organic Chemistry 2014, 5456-5461.
Abstract:
New diazocines as photochromic switches for the surface functionalization via the “platform approach” were synthesized and characterized. Symmetric diazocines as well as asymmetric molecules based on an indane scaffold were obtained and their photochromic properties were investigated. In a final step, the diazocines were mounted on molecular platforms (triazatriangulenium ions).
BibTeX:
@article{Tellkamp2014,
author = {Tellkamp, Tobias and Shen, Jun and Okamoto, Yoshio and Herges, Rainer},
title = {Diazocines on Molecular Platforms},
journal = {European Journal of Organic Chemistry},
publisher = {WILEY-VCH Verlag},
year = {2014},
pages = {5456-5461},
doi = {http://doi.org/10.1002/ejoc.201402541}
}
Core-Modified Rubyrins Containing Dithienylethene Moieties.
Z. Zhou, Y. Chang, S. Shimizu, J. Mack, C. Schuett, R. Herges, Z. Shen and N. Kobayashi, Angew. Chem., Int. Ed. 2014, 53, 6563-6567.
Abstract:
Two stable core-modified rubyrins bearing one and two dithienylethene (DTE) units (1 and 2) have been synthesized. With one "closed-form" DTE unit, 1 shows aromaticity assocd. with its conjugated circuit of 26 π-electrons. In contrast, rubyrin 2 contg. one "open-form" DTE unit has nonarom. properties.
BibTeX:
@article{Zhou2014,
author = {Zhou, Zhikuan and Chang, Yi and Shimizu, Soji and Mack, John and Schuett, Christian and Herges, Rainer and Shen, Zhen and Kobayashi, Nagao.},
title = {Core-Modified Rubyrins Containing Dithienylethene Moieties.},
journal = {Angew. Chem., Int. Ed.},
year = {2014},
volume = {53},
number = { },
pages = {6563-6567},
doi = {http://doi.org/10.1002/anie.201402711}
}
Thermochemistry and photochemistry of spiroketals derived from indan-2-one: stepwise processes versus coarctate fragmentations.
G. Bucher, G. Heitmann and R. Herges, Beilstein J. Org. Chem. 2013, 9, 1668-1676.
Abstract:
Coarctate reactions are defined as reactions that include atoms at which two bonds are made and two bonds are broken simultaneously. In the pursuit of the discovery of new coarctate reactions we investigate the fragmentation reactions of cyclic ketals. Three ketals with different ring sizes derived from indan-2-one were decompd. by photolysis and pyrolysis. Particularly clean is the photolysis of the indan-2-one ketal 1, which gives o-quinodimethane, carbon dioxide and ethylene. The mechanism formally corresponds to a photochem. allowed coarctate fragmentation. Pyrolysis of the five-ring ketal yields a no. of products. This is in agreement with the fact that coarctate fragmentation obsd. upon irradn. would be thermochem. forbidden, although this exclusion principle does not hold for chelotropic reactions. In contrast, fragmentation of the seven-ring ketal 3 is thermochem. allowed and photochem. forbidden. Upon pyrolysis of 3 several products were isolated that could be explained by a coarctate fragmentation. However, the reaction is less clean and stepwise mechanisms may compete.
BibTeX:
@article{Bucher2013,
author = {Bucher, Goetz and Heitmann, Gernot and Herges, Rainer.},
title = {Thermochemistry and photochemistry of spiroketals derived from indan-2-one: stepwise processes versus coarctate fragmentations.},
journal = {Beilstein J. Org. Chem.},
year = {2013},
volume = {9},
number = { },
pages = {1668-1676},
doi = {http://doi.org/10.3762/bjoc.9.191}
}
Surface Control of Alkyl Chain Conformations and 2D Chiral Amplification
N. Hauptmann, K. Scheil, T.G. Gopakumar, F.L. Otte, C. Schütt, R. Herges and R. Berndt, Journal of the American Chemical Society 2013, 135, 8814-8817.
Abstract:
Trioctyl-functionalized triazatriangulenium (trioctyl-TATA) deposited on Au(111) and Ag(111) surfaces by electrospray ionization was investigated using low-temperature scanning tunneling microscopy. The molecule surprisingly adsorbs with gauche rather than anti conformations of the octyl groups. We observed chiral amplification in the islands. Only one of the eight possible configurations of the octyl groups was found in homochiral hexagonal networks. Quantum-chemical calculations confirmed and explained the preference for the gauche conformations of adsorbed trioctyl-TATA.
BibTeX:
@article{Hauptmann2013,
author = {Hauptmann, Nadine and Scheil, Katharina and Gopakumar, Thiruvancheril G. and Otte, Franziska L. and Schütt, Christian and Herges, Rainer and Berndt, Richard},
title = {Surface Control of Alkyl Chain Conformations and 2D Chiral Amplification},
journal = {Journal of the American Chemical Society},
year = {2013},
volume = {135},
pages = {8814-8817},
doi = {http://doi.org/10.1021/ja4036187}
}
Studies of the molecular switching of azobenzene-functionalized platform adlayers on Au(1 1 1) by chronoamperometry.
U. Jung, J. Kubitschke, R. Herges and O. Magnussen, Electrochim. Acta 2013, 112, 869-880.
Abstract:
Photochronoamperometry is introduced as a new approach to study isomerization reactions in photoswitchable mol. adsorbate layers on metal electrodes. Using highly ordered self-assembled monolayers of mol. platforms with freestanding vertical azobenzene functionalities on single-cryst. Au(1 1 1) as an example, the photoinduced current response was measured as a function of potential and irradn. intensity and compared to complementary cyclic voltammetry studies. The obsd. behavior is discussed within a kinetical model that qual. describes the exptl. findings. In order to describe the intensity dependence, the isomerization reactions, in particular, the thermal relaxation, have to occur distinctively faster than the electrochem. processes, which is in good agreement with previous results for these photoswitchable adlayers.
BibTeX:
@article{Jung,
author = {Jung, Ulrich and Kubitschke, Jens and Herges, Rainer and Magnussen, Olaf.},
title = {Studies of the molecular switching of azobenzene-functionalized platform adlayers on Au(1 1 1) by chronoamperometry.},
journal = {Electrochim. Acta},
year = {2013},
volume = {112},
number = { },
pages = {869-880},
doi = {http://doi.org/10.1016/j.electacta.2013.06.123}
}
The synthesis and characterization of a belt-shaped carbon nanoring.
A.R. Mohebbi, R. Herges, H.R. Darabi, S.M. Nasseri and C. Nather, Curr. Org. Chem. 2013, 17, 926-929.
Abstract:
Arom. belts are hoop-shaped, π-conjugated macrocyclic compds. that form the fundamental annular segments of single-walled carbon nanotubes (SWCNTs). Syntheses of carbon nanomaterials (belt-shaped nanomaterials) have been challenging the chem. community for several decades. The main reason probably is the possibility that their prepn. could open the way to a rational chem. synthesis carbon nanotubes. Here, the authors reported a successful synthesis of a belt-shaped carbon nanoring, namely cyclic [6]dianthryltetraphenylacetylene ([6]CAPA), including two anthracene-acetylene and four phenylacetylene units. The synthesis of the target compd. (I) was achieved in a six-step synthesis by formation of cyclic [6]dianthryltetraphenylethylene ([6]CAPE), with[36]annulene periphery.
BibTeX:
@article{Mohebbi2013,
author = {Mohebbi, Ali Reza and Herges, Rainer and Darabi, Hossein Reza and Nasseri, Sareh M. and Nather, Christian.},
title = {The synthesis and characterization of a belt-shaped carbon nanoring.},
journal = {Curr. Org. Chem.},
year = {2013},
volume = {17},
number = { },
pages = {926-929},
doi = {http://doi.org/10.2174/1385272811317090006}
}
Localized Surface Plasmon Resonance Investigations of Photoswitching in Azobenzene-Functionalized Self-Assembled Monolayers on Au.
M. Mueller, U. Jung, V. Gusak, S. Ulrich, M. Holz, R. Herges, C. Langhammer and O. Magnussen, Langmuir 2013, 29, 10693-10699.
Abstract:
Localized plasmon resonance (LSPR) spectroscopy, employing gold nanodisk substrates, was applied for studies of photoswitching in self-assembled monolayers of azobenzene-contg. thiols. By choosing customized samples in which the sharp LSPR resonance is well sepd. from the spectral regime of the mol. absorption bands, the photoisomerization kinetics of the adlayer can be monitored in real time. Quant. data on the photoinduced trans-cis and cis-trans isomerization processes in inert gas atm. were obtained as a function of irradn. intensity and temp., demonstrating the high sensitivity of this technique to such processes in functional adlayers.
BibTeX:
@article{Mueller2013,
author = {Mueller, Mathias and Jung, Ulrich and Gusak, Viktoria and Ulrich, Sandra and Holz, Michelle and Herges, Rainer and Langhammer, Christoph and Magnussen, Olaf.},
title = {Localized Surface Plasmon Resonance Investigations of Photoswitching in Azobenzene-Functionalized Self-Assembled Monolayers on Au.},
journal = {Langmuir},
year = {2013},
volume = {29},
number = { },
pages = {10693-10699},
doi = {http://doi.org/10.1021/la401825f}
}
Moebius molecules with twists and writhes.
G.R. Schaller and R. Herges, Chem. Commun. 2013, 49, 1254-1260.
Abstract:
A review. The Moebius topol. inspired science and arts for many centuries. In chem. interest was stimulated by Heilbronner almost 50 years ago when he predicted that Moebius annulenes would violate the Hueckel rule. A no. of theor. papers followed but it was not until 2003 when the first synthesis of an arom. Moebius structure was accomplished. Inspired by the recent progress, the concept of Moebius topol. has gained further momentum in synthesis as well as theory. The authors present a topol. description of Moebius mols., and strategies for the design and synthesis of these structures.
BibTeX:
@article{Schaller2013,
author = {Schaller, Gaston R. and Herges, Rainer.},
title = {Moebius molecules with twists and writhes.},
journal = {Chem. Commun.},
year = {2013},
volume = {49},
number = { },
pages = {1254-1260},
doi = {http://doi.org/10.1039/c2cc34763f}
}
Amino-substituted diazocines as pincer-type photochromic switches
H. Sell, C. Näther and R. Herges, Beilstein Journal of Organic Chemistry 2013, 9, 1-7.
Abstract:
Azobenzenes are robust, reliable, and easy to synthesize photochromic switches. However, their high conformational flexibility is a disadvantage in machine-like applications. The almost free rotation of the phenyl groups can be restricted by bridging two ortho positions with a CH2CH2 group, as realized in the dihydrodibenzo diazocine framework. We present the synthesis and properties of 3,3’-amino- and 3,3’-acetamido substituted diazocines. Upon irradiation with light of 405 and 530 nm they isomerize from the cis to the trans configuration and back, and thereby perform a pincer-like motion. In the thermodynamically more stable cis isomer the lone pairs of the amino nitrogen atoms point towards each other, and in the trans form they point in opposite directions. The distance between the amino nitrogen atoms changes between 8 Å (cis) and 11 Å (trans isomer)
BibTeX:
@article{Sell2013,
author = {Hanno Sell and Christian Näther and Rainer Herges},
title = {Amino-substituted diazocines as pincer-type photochromic switches},
journal = {Beilstein Journal of Organic Chemistry},
year = {2013},
volume = {9},
pages = {1-7},
doi = {http://doi.org/10.3762/bjoc.9.1}
}
Doubly Coarctate-Stabilized Carbenes: Synthetic and Computational Studies.
B.S. Young, R. Herges and M.M. Haley, J. Org. Chem. 2013, 78, 1977-1983.
Abstract:
Isoindazoles joined by an ethynyl linker to either a phenyltriazene or a phenyldiazene moiety were synthesized, and their subsequent reactivity was examd. Computations suggest that these mols. could rearrange at moderate temps. via carbene intermediates that are doubly stabilized by coarctate conjugation. The exptl. results corroborate the calcns., as the transient carbene can either be trapped with oxygen or undergo ring-opening to afford a rearranged product. Addnl. calcns. illustrate some design principles that might lead to stable carbenes that are the global min. on the coarctate hypersurface.
BibTeX:
@article{Young2013,
author = {Young, Brian S. and Herges, Rainer and Haley, Michael M.},
title = {Doubly Coarctate-Stabilized Carbenes: Synthetic and Computational Studies.},
journal = {J. Org. Chem.},
year = {2013},
volume = {78},
number = { },
pages = {1977-1983},
doi = {http://doi.org/10.1021/jo3020374}
}
FeIII Spin-Crossover Complexes with Photoisomerizable Ligands: Experimental and Theoretical Studies on the Ligand-Driven Light-Induced Spin Change Effect
A. Bannwarth, S.O. Schmidt, G. Peters, F.D. Sönnichsen, W. Thimm, R. Herges and F. Tuczek, Eur. J. Inorg. Chem. 2012, 2776-2783.
Abstract:
Conflicting results have been reported with respect to the photoinduced switching of the magnetic properties of [FeIII(salten)]+ complexes [salten = 4-azaheptamethylene-1,7-bis(salicylideneiminate)] coordinated by photoisomerizable ligands. In order to address this problem, two FeIII complexes [Fe(salten)(3-azpy)]BPh4 (1) and [Fe(salten)(4-azpy)]BPh4 (2) have been synthesized and characterized by various physicochemical methods (azpy = phenylazopyridine). Both 1 and 2 exhibit a low spin (S = 1/2) to high spin (HS, S = 5/2) transition in the solid state. In solution at room temperature both complexes are predominantly HS. Upon exposure to 310 (trans-cis) and 440 nm radiation (cis-trans) the free and coordinated 3- and 4-azpy ligands undergo a reversible cis–trans isomerization. For 2 a corresponding reduction of the HS fraction 2 % is observed, whereas in 1 no effect is observed. Extensive DFT calculations, which employ different functionals and basis sets, explain this experimental result. The consequences of these findings with respect to the design of spin-switchable iron(III) complexes with photoactive ligands are discussed.
BibTeX:
@article{Bannwarth2012,
author = {Bannwarth, Alexander and Schmidt,Sven Olaf and Peters, Gerhard and Sönnichsen, Frank D. and Thimm, Wulf and Herges, Rainer and Tuczek, Felix},
title = {FeIII Spin-Crossover Complexes with Photoisomerizable Ligands: Experimental and Theoretical Studies on the Ligand-Driven Light-Induced Spin Change Effect},
journal = {Eur. J. Inorg. Chem.},
year = {2012},
pages = {2776-2783},
doi = {http://doi.org/10.1002/ejic.201101227}
}
A 20π-Electron Heteroporphyrin Containing a Thienopyrrole Unit
Y. Chang, H. Chen, Z. Zhou, Y. Zhang, C. Schütt, R. Herges and Z. Shen, Angewandte Chemie 2012, 124, 12973-12977.
Abstract:
Ein Heteroporphyrin mit einer Thienopyrrol-Einheit wurde hergestellt, dessen nichtaromatischer Charakter klar durch UV/Vis-Absorption, 1H-NMR-Spektroskopie und theoretische Studien nachgewiesen wurde. Eine Einkristall-Röntgenstrukturanalyse zeigt, dass das Molekül eine ebene Konformation einnimmt, in der die äußeren C-C-Bindungslängen des Makrocyclus deutlich abwechseln.
BibTeX:
@article{Chang2012,
author = {Chang, Yi and Chen, Huachao and Zhou, Zhikuan and Zhang, Yue and Schütt, Christian and Herges, Rainer and Shen, Zhen},
title = {A 20π-Electron Heteroporphyrin Containing a Thienopyrrole Unit},
journal = {Angewandte Chemie},
publisher = {WILEY-VCH Verlag},
year = {2012},
volume = {124},
pages = {12973-12977},
doi = {http://doi.org/10.1002/ange.201204954}
}
Cup-shaped E,E-stilbenophane: synthesis, crystal structure and supramolecular chemistry.
H.R. Darabi, A. Darestani Farahani, M. Hashemi Karouei, K. Aghapoor, R. Firouzi, R. Herges, A.R. Mohebbi and C. Nather, Supramol. Chem. 2012, 24, 653-657.
Abstract:
A new E,E-stilbenophane was synthesized and characterized. The crystal structure of this cyclophane shows that this mol. has a cup-shaped structure, which hosts a Ph ring of neighboring mol. as guest in its cavity with a π-π distance of about 3.7 Å. Moreover, the NMR spectra and theor. anal. (gauge-independent AOs (GIAO) and quantum theory of atoms in mols. (QTAIM)) suggest that the silver recognition by E,E-stilbenophane host mols. is based on cation-π interactions in which the π-electrons of the double bonds play a major role.
BibTeX:
@article{Darabi2012,
author = {Darabi, Hossein Reza and Darestani Farahani, Abbas and Hashemi Karouei, Mohammad and Aghapoor, Kioumars and Firouzi, Rohoullah and Herges, Rainer and Mohebbi, Ali Reza and Nather, Christian.},
title = {Cup-shaped E,E-stilbenophane: synthesis, crystal structure and supramolecular chemistry.},
journal = {Supramol. Chem.},
year = {2012},
volume = {24},
number = { },
pages = {653-657},
doi = {http://doi.org/10.1080/10610278.2012.678359}
}
Electronic Ground-State and Orbital Ordering of Iron Phthalocyanine on H/Si(111) Unraveled by Spatially Resolved Tunneling Spectroscopy
M. Gruyters, T. Pingel, T.G. Gopakumar, N. Néel, C. Schütt, F. Köhler, R. Herges and R. Berndt, The Journal of Physical Chemistry C 2012, 116, 20882-20886.
Abstract:
The electronic properties of FePc molecules adsorbed on hydrogen-passivated Si(111) surfaces are investigated by scanning tunneling microscopy at low temperatures. Spatially resolved spectroscopy reveals a significant variation of the electronic states at different positions above the molecule. The highest occupied ligand- and metal-based orbitals of FePc are determined by pronounced peaks in the tunneling spectra and voltage-dependent changes in the microscopic images. Comparison with density functional theory calculations indicates that the electronic ground state is an 3A1g state.
BibTeX:
@article{Gruyters2012,
author = {Gruyters, M. and Pingel, T. and Gopakumar, T. G. and Néel, N. and Schütt, Ch. and Köhler, F. and Herges, R. and Berndt, R.},
title = {Electronic Ground-State and Orbital Ordering of Iron Phthalocyanine on H/Si(111) Unraveled by Spatially Resolved Tunneling Spectroscopy},
journal = {The Journal of Physical Chemistry C},
year = {2012},
volume = {116},
number = {39},
pages = {20882-20886},
doi = {http://doi.org/10.1021/jp3058433}
}
Reversible switching in self-assembled monolayers of azobenzene thiolates on Au (111) probed by threshold photoemission.
N. Heinemann, J. Grunau, T. Leissner, O. Andreyev, S. Kuhn, U. Jung, D. Zargarani, R. Herges, O. Magnussen and M. Bauer, Chem. Phys. 2012, 402, 22-28.
Abstract:
The reversible photo- and thermally activated isomerization of the mol. switch 3-(4-(4-Hexyl-phenylazo)-phenoxy)-propane-1-thiol (ABT, short for AzoBenzeneThiol) deposited by self-assembly from soln. on Au (111) was studied using laser-based photoelectron spectroscopy. Differences in the mol. dipole moment characteristic for the trans and the cis isomer of ABT were monitored via changes in the sample work function, accessible by detection of the threshold energy for photoemission. A quant. anal. of the authors' data shows that the fraction of mols. within the densely packed monolayer that undergoes a switching process is of the order of 1%. This result indicates the relevance of substrate and film defects required to overcome the steric or electronic hindrance of the isomerization reaction in a densely packed monolayer.
BibTeX:
@article{Heinemann2012,
author = {Heinemann, Nils and Grunau, Jan and Leissner, Till and Andreyev, Oleksiy and Kuhn, Sonja and Jung, Ulrich and Zargarani, Dordaneh and Herges, Rainer and Magnussen, Olaf and Bauer, Michael.},
title = {Reversible switching in self-assembled monolayers of azobenzene thiolates on Au (111) probed by threshold photoemission.},
journal = {Chem. Phys.},
year = {2012},
volume = {402},
pages = {22-28},
doi = {http://doi.org/10.1016/j.chemphys.2012.03.025}
}
Molecular Switch
R. Herges, O. Jansen, F. Tuczek and S. Venkatamarani, PCT Int. Appl., 2012, .
Abstract:
Photosensitive molecular switch, having a chelate ligand, a metal ion bonded coordinatively to the chelate ligand, the metal ion being selected from the group of metal ions consisting of Mn2+, Mn3+, Fe2+, Fe3+, Co2+ and ?i2+, a photochromic system which is bonded covalently to the chelate ligand and can be isomerized by irradiation, this system being bonded coordinatively to the metal ion in one configuration and not bonded to the metal ion in the other configuration.
BibTeX:
@patent{Herges2012,
author = {Herges, Rainer and Jansen, Olav and Tuczek, Felix and Venkatamarani, Sugumar},
title = {Molecular Switch},
year = {2012},
number = {WO 2012022299 A1 20120223.},
url = {http://worldwide.espacenet.com/publicationDetails/biblio?CC=WO&NR=2012022299&KC=&FT=E&locale=en_EP}
}
Photosensitive metal porphyrin complexes with pendant photoisomerizable chelate arm as photochromic molecular switches undergoing photoinduced spin transition.
R. Herges, O. Jansen, F. Tuczek and S. Venkatamarani, Ger. Offen., 2012, .
BibTeX:
@patent{Herges2012a,
author = {Herges, Rainer and Jansen, Olav and Tuczek, Felix and Venkatamarani, Sugumar},
title = {Photosensitive metal porphyrin complexes with pendant photoisomerizable chelate arm as photochromic molecular switches undergoing photoinduced spin transition.},
year = {2012},
number = {DE 102010034496 A1 20120216.}
}
The growth and electronic structure of azobenzene-based functional molecules on layered crystals.
J. Iwicki, E. Ludwig, J. Buck, M. Kallaene, F. Koehler, R. Herges, L. Kipp and K. Rossnagel, J. Phys.: Condens. Matter 2012, 24, 394011/1-394011/7.
Abstract:
In situ UPS is used to study the growth of ultrathin films of azobenzene-based functional mols. (azobenzene, Disperse Orange 3, and a triazatriangulenium platform with an attached functional azo-group) on the layered metal TiTe2 and on the layered semiconductor HfS2 at liq. nitrogen temps. Effects of intermol. interactions, of the substrate electronic structure, and of the thermal energy of the sublimated mols. on the growth process and on the adsorbate electronic structure are identified and discussed. A weak adsorbate-substrate interaction is particularly obsd. for the layered semiconducting substrate, holding the promise of efficient mol. photo-switching.
BibTeX:
@article{Iwicki2012,
author = {Iwicki, J. and Ludwig, E. and Buck, J. and Kallaene, M. and Koehler, F. and Herges, R. and Kipp, L. and Rossnagel, K.},
title = {The growth and electronic structure of azobenzene-based functional molecules on layered crystals.},
journal = {J. Phys.: Condens. Matter},
year = {2012},
volume = {24},
number = { },
pages = {394011/1-394011/7},
doi = {http://doi.org/10.1088/0953-8984/24/39/394011}
}
Photoswitching of Azobenzene-Functionalized Molecular Platforms on Au Surfaces
U. Jung, C. Schütt, O. Filinova, J. Kubitschke, R. Herges and O. Magnussen, The Journal of Physical Chemistry C 2012, 116, 25943-25948.
Abstract:
The photo- and thermally induced switching of well-ordered molecular arrays of free-standing functional groups, formed by self-assembly on Au surfaces, were studied by photoelectrochemical methods (cyclic voltammetry, chronoamperometry) and surface plasmon resonance spectroscopy. These molecular adlayers exhibit azobenzene functions mounted vertically on the surface via molecular platforms on the basis of triazatriangulenium. Detailed quantitative studies of the switching kinetics revealed that the photoinduced trans–cis isomerization of the azobenzene groups in these adlayers proceeds very fast and highly reversible. Cis–trans backisomerization by thermal relaxation occurs surprisingly 4–5 orders of magnitude faster than in solution. A rapid thermal cis–trans relaxation that dominates over the photoinduced processes is also supported by the pronounced increase of the cis fraction in the adlayers with irradiation intensity and the weak dependence of the isomerization time constants on the intensity. In complementary density functional theory calculations of the cis isomer on a Au cluster, no significant electron density depletion of the azo moiety, but strong electronic coupling of the switchable group with the Au substrate, were found. We propose that the latter leads to a spin exchange between conduction electrons in the metal and the azo moiety, enabling a relaxation mechanism that is forbidden for the free molecule.
BibTeX:
@article{Jung2012,
author = {Jung, Ulrich and Schütt, Christian and Filinova, Olena and Kubitschke, Jens and Herges, Rainer and Magnussen, Olaf},
title = {Photoswitching of Azobenzene-Functionalized Molecular Platforms on Au Surfaces},
journal = {The Journal of Physical Chemistry C},
year = {2012},
volume = {116},
pages = {25943-25948},
doi = {http://doi.org/10.1021/jp310451c}
}
Introducing a photo-switchable azo-functionality inside Cr-MIL-101-NH2 by covalent post-synthetic modification.
A. Modrow, D. Zargarani, R. Herges and N. Stock, Dalton Trans. 2012, 41, 8690-8696.
Abstract:
For the first time an azo functionality was covalently introduced into a MOF by post-synthetic modification. The reaction of Cr-MIL-101-NH2, [Cr3(μ3-O)(OH)(H2O)2(O2CC6NH5CO2)3]·nH2O, with p-phenylazobenzoylchloride (1) and 4-(phenylazo)Ph isocyanate (2) as the reactants led to the compds. Cr-MIL-101amide and Cr-MIL-101urea, with the azo groups protruding into the mesoporous cages. XRPD and N2 sorption measurements confirm the intactness of the framework and the successful covalent modification was proven by IR- and NMR-spectroscopy. Also, cis/trans isomerization upon irradn. with light was demonstrated by UV/visible spectroscopy. More distinct changes in the UV/visible spectra were obsd. for Cr-MIL-101amide compared to Cr-MIL-101urea, while the degree of functionalization, i.e. the no. of reacted NH2-groups, seems to have a less pronounced effect. The variation of the sorption properties due to the cis/trans isomerization was proven by methane adsorption measurements.
BibTeX:
@article{Modrow2012,
author = {Modrow, Antje and Zargarani, Dordaneh and Herges, Rainer and Stock, Norbert.},
title = {Introducing a photo-switchable azo-functionality inside Cr-MIL-101-NH2 by covalent post-synthetic modification.},
journal = {Dalton Trans.},
year = {2012},
volume = {41},
pages = {8690-8696},
doi = {http://doi.org/10.1039/C2DT30672G}
}
Systematic Investigation of Porous Inorganic-Organic Hybrid Compounds with Photo-Switchable Properties
A. Modrow, M. Feyand, D. Zargarani, R. Herges and N. Stock, Zeitschrift für anorganische und allgemeine Chemie 2012, 638, 2138-2143.
Abstract:
Four new compounds [Co2(NDC)2(AzBIPY)] (1), [Cu2(NDC)2(AzBIPY)] (2), [Zn2(BPDC)2(AzBIPY)] (3) and [Zn2(CCA)2(AzBIPY)] (4) (with H2NDC: 2, 6-naphthalenedicarboxylic acid, AzBIPY: 3-azo-phenyl-4, 4′-bipyridine, H2BPDC: 4, 4′-biphenyl-dicarboxylic acid and H2CCA: 4-carboxy-cinnamic acid) were synthesized and characterized. All compounds have paddle-wheel units and photo switchable linker molecules in common. In all four compounds the azo group of the AzBIPY linker molecule protrudes into the pores. For compound 1 and 2 isomerization can be accomplished upon irradiation with UV light (λ = 365 nm) to switch the thermodynamically stable trans-isomer into the cis-isomer. Back switching can be achieved thermally or by irradiation with visible light (λ = 455 nm).
BibTeX:
@article{Modrow2012a,
author = {Modrow, Antje and Feyand, Mark and Zargarani, Dordaneh and Herges, Rainer and Stock, Norbert},
title = {Systematic Investigation of Porous Inorganic-Organic Hybrid Compounds with Photo-Switchable Properties},
journal = {Zeitschrift für anorganische und allgemeine Chemie},
publisher = {WILEY-VCH Verlag},
year = {2012},
volume = {638},
pages = {2138-2143},
doi = {http://doi.org/10.1002/zaac.201200048}
}
Fragments of Fullerenes and Carbon Nanotubes: Designed Synthesis, Unusual Reactions, and Coordination Chemistry
G.R. Schaller and R. Herges, In Fragm. Fullerenes Carbon Nanotubes. 2012, 259-289.
Abstract:
A review. The rational synthesis of carbon nanotubes is one of the most challenging and yet unsolved problems of nonnatural product synthesis. Several approaches were pursued towards this end starting from smaller precursors: (a) fullerene hemispheres, (b) concave building blocks, and (c) mol. belts. Achievements, current status and prospects of the different strategies are described.
BibTeX:
@inbook{Schaller2012,
author = {Schaller, Gaston R. and Herges, Rainer},
title = {Fragments of Fullerenes and Carbon Nanotubes: Designed Synthesis, Unusual Reactions, and Coordination Chemistry},
booktitle = {Fragm. Fullerenes Carbon Nanotubes},
publisher = {John Wiley & Sons, Inc.},
year = {2012},
number = { },
pages = {259-289},
doi = {http://doi.org/10.1002/9781118011263.ch10}
}
Thermodynamic and kinetic stabilization of divanadate in the monovanadate/divanadate equilibrium using a Zn-cyclene derivative: Towards a simple ATP synthase model
H. Sell, A. Gehl, F.D. Sönnichsen and R. Herges, Beilstein J. Org. Chem 2012, 8, 81-89.
Abstract:
For the condensation of anions such as phosphate and ADP to form ATP and water, nature employs sophisticated supramolecular systems to overcome coulomb repulsion and activation barriers. For an attempt to create a simple, analogous chemical system, the dimerization of vanadate is probably the simplest model. We have investigated Zn-benzylcyclene which favors the dimerization thermodynamically as shown by NMR titration. Moreover, EXSY NMR experiments reveal that the vanadate dimer is also kinetically stabilized with respect to hydrolysis by complexation with Zn-cyclene.
BibTeX:
@article{Sell2012,
author = {Sell, Hanno and Gehl, Anika and Sönnichsen, Frank D. and Herges, Rainer},
title = {Thermodynamic and kinetic stabilization of divanadate in the monovanadate/divanadate equilibrium using a Zn-cyclene derivative: Towards a simple ATP synthase model},
journal = {Beilstein J. Org. Chem},
year = {2012},
volume = {8},
pages = {81-89},
doi = {http://doi.org/10.3762/bjoc.8.8}
}
Bis(4-methoxypyridin-3-yl)diazene.
S. Thies, C. Naether and R. Herges, Acta Crystallogr., Sect. E: Struct. Rep. Online 2012, E68, o1568.
Abstract:
The asym. unit of the title compd., C12H12N4O2, consists of one half-mol., which is located on a center of inversion. The mol. has a step-like shape; the azo group adopting a trans configuration, with the pyridine rings being parallel-displace.
BibTeX:
@article{Thies2012,
author = {Thies, Steffen and Naether, Christian and Herges, Rainer.},
title = {Bis(4-methoxypyridin-3-yl)diazene.},
journal = {Acta Crystallogr., Sect. E: Struct. Rep. Online},
year = {2012},
volume = {E68},
pages = {o1568},
doi = {http://doi.org/10.1107/S1600536812018326}
}
Light-Driven Coordination-Induced Spin-State Switching: Rational Design of Photodissociable Ligands
S. Thies, H. Sell, C. Bornholdt, C. Schütt, F. Köhler, F. Tuczek and R. Herges, Chemistry – A European Journal 2012, 18, 16358-16368.
Abstract:
The bistability of spin states (e.g., spin crossover) in bulk materials is well investigated and understood. We recently extended spin-state switching to isolated molecules at room temperature (light-driven coordination-induced spin-state switching, or LD-CISSS). Whereas bistability and hysteresis in conventional spin-crossover materials are caused by cooperative effects in the crystal lattice, spin switching in LD-CISSS is achieved by reversibly changing the coordination number of a metal complex by means of a photochromic ligand that binds in one configuration but dissociates in the other form. We present mathematical proof that the maximum efficiency in property switching by such a photodissociable ligand (PDL) is only dependent on the ratio of the association constants of both configurations. Rational design by using DFT calculations was applied to develop a photoswitchable ligand with a high switching efficiency. The starting point was a nickel–porphyrin as the transition-metal complex and 3-phenylazopyridine as the photodissociable ligand. Calculations and experiments were performed in two iterative steps to find a substitution pattern at the phenylazopyridine ligand that provided optimum performance. Following this strategy, we synthesized an improved photodissociable ligand that binds to the Ni–porphyrin with an association constant that is 5.36 times higher in its trans form than in the cis form. The switching efficiency between the diamagnetic and paramagnetic state is efficient as well (72 % paramagnetic Ni–porphyrin after irradiation at 365 nm, 32 % paramagnetic species after irradiation at 440 nm). Potential applications arise from the fact that the LD-CISSS approach for the first time allows reversible switching of the magnetic susceptibility of a homogeneous solution. Photoswitchable contrast agents for magnetic resonance imaging and light-controlled magnetic levitation are conceivable applications.
BibTeX:
@article{Thies2012a,
author = {Thies, Steffen and Sell, Hanno and Bornholdt, Claudia and Schütt, Christian and Köhler, Felix and Tuczek, Felix and Herges, Rainer},
title = {Light-Driven Coordination-Induced Spin-State Switching: Rational Design of Photodissociable Ligands},
journal = {Chemistry – A European Journal},
publisher = {WILEY-VCH Verlag},
year = {2012},
volume = {18},
pages = {16358-16368},
doi = {http://doi.org/10.1002/chem.201201698}
}
Photoswitchable Azoheterocycles via Coupling of Lithiated Imidazoles with Benzenediazonium Salts
T. Wendler, C. Schütt, C. Näther and R. Herges, The Journal of Organic Chemistry 2012, 77, 3284-3287.
Abstract:
In contrast to azobenzenes, heterocyclic azo compounds are less well investigated. Phenylazoimidazoles would be versatile as photodissociable ligands (PDLs) because imidazole is an important donor in coordination chemistry. Here, we present the synthesis of 4- and 5-phenylazoimidazoles via a novel azo-coupling method. 1,2-Protected imidazole is lithiated in the 5-position and coupled with benzenediazonium tetrafluoroborate. Several new phenylazoimidazoles were prepared. They exhibit an excellent switching behavior. Upon irradiation of the trans isomers with UV light, >95% of the cis forms are obtained. Upon heating, a complete transformation back to the trans configuration was achieved. Back switching with visible light, however, is incomplete.
BibTeX:
@article{Wendler2012,
author = {Wendler, Thore and Schütt, Christian and Näther, Christian and Herges, Rainer},
title = {Photoswitchable Azoheterocycles via Coupling of Lithiated Imidazoles with Benzenediazonium Salts},
journal = {The Journal of Organic Chemistry},
year = {2012},
volume = {77},
number = {7},
pages = {3284-3287},
doi = {http://doi.org/10.1021/jo202688x}
}
Tetrakis(diisopropyl amide) substituted norbornadiene and quadricyclane are highly barium selective ligands
T. Winkler, M. Bayrhuber, B. Sahlmann and R. Herges, Dalton Trans. 2012, 41, 7037-7040.
Abstract:
Tetrakis(diisopropyl amide) substituted norbornadiene and quadricyclane derivatives were investigated for their extraction and transport capabilities with alkaline earth metal cations. Both amides exhibited a remarkably high preference of Ba2+ over any other alkali metal or alkaline earth cation. The binding geometries were determined by quantum chemical DFT calculations.
BibTeX:
@article{Winkler2012,
author = {Winkler, Torsten and Bayrhuber, Monika and Sahlmann, Benjamin and Herges, Rainer},
title = {Tetrakis(diisopropyl amide) substituted norbornadiene and quadricyclane are highly barium selective ligands},
journal = {Dalton Trans.},
publisher = {The Royal Society of Chemistry},
year = {2012},
volume = {41},
pages = {7037-7040},
doi = {http://doi.org/10.1039/C2DT30242J}
}
Coarctate cyclization reactions: a primer
B.S. Young, R. Herges and M.M. Haley, Chem Commun 2012, 48, 9441-9455.
Abstract:
The cleavage of five-membered heterocycles possessing an exocyclic carbene or nitrene to form conjugated ene-ene-yne systems has been documented for over 40 years; however, the reverse reaction, using a conjugated "ene-ene-yne" precursor to form a heterocycle is a relatively new approach. Over the past decade, the Haley and Herges groups have studied computationally and experimentally the cyclization of the "hetero-ene-ene-yne" motif via an unusual class of concerted reactions known as coarctate reactions. This feature article details our synthetic and mechanistic work involving triazene-arene-alkynes and structurally-related systems to generate heterocycles using coarctate chemistry.
BibTeX:
@article{Young2012,
author = {Young, Brian S. and Herges, Rainer and Haley, Michael M.},
title = {Coarctate cyclization reactions: a primer},
journal = {Chem Commun},
year = {2012},
volume = {48},
pages = {9441-9455},
doi = {http://doi.org/10.1039/C2CC34026G}
}
Experimental and Theoretical Characterization of the Aromatization, Epimerization, and Fragmentation Reactions of Bi-2H-azirin-2-yls Prepared from 1,4-Diazidobuta-1,3-dienes.
K. Banert, F. Koehler, A. Melzer, I. Scharf, G. Rheinwald, T. Rueffer, H. Lang, R. Herges, K. Hess, N. Ghavtadze and E.-U. Wuerthwein, Chem. Eur. J. 2011, 17, 10071-10080.
Abstract:
1,4-Diazidobuta-1,3-dienes (Z,Z)-10, 17, and 21 were photolyzed and thermolyzed to yield the pyridazines 13, 20, and 23, resp. To explain these arom. final products, the generation of highly strained bi-2H-azirin-2-yls 12, 19, and 22 and their valence isomerization were postulated. In the case of meso- and rac-22, nearly quant. formation from diazide 21, isolation as stable solids, and complete characterization were possible. On the thermolysis of 22, aromatization to 23 was only a side reaction, whereas equilibration of meso- and rac-22 and fragmentation, which led to alkyne 24 and acetonitrile, dominated. Prolonged irradn. of 22 gave mainly the pyrimidine 25. The change of the configuration at C-2 of the 2H-azirine unit was obsd. not only in the case of bi-2H-azirin-2-yls 22 but also for simple spirocyclic 2H-azirines 29 at a relatively low temp. (75 °C). The fragmentation of rac-22 to give alkyne 24 and two mols. of acetonitrile was also studied by high-level quantum chem. calcns. For a related model system 30 (Me instead of Ph groups), two transition states TS-30-31 of comparable energy with multiconfigurational electronic states could be localized on the energy hypersurface for this one-step conversion. The sym. transition state complies with the definition of a coarctate mechanism.
BibTeX:
@article{Banert2011,
author = {Banert, Klaus and Koehler, Frank and Melzer, Antje and Scharf, Ingolf and Rheinwald, Gerd and Rueffer, Tobias and Lang, Heinrich and Herges, Rainer and Hess, Kirsten and Ghavtadze, Nugzar and Wuerthwein, Ernst-Ulrich.},
title = {Experimental and Theoretical Characterization of the Aromatization, Epimerization, and Fragmentation Reactions of Bi-2H-azirin-2-yls Prepared from 1,4-Diazidobuta-1,3-dienes.},
journal = {Chem. Eur. J.},
year = {2011},
volume = {17},
number = { },
pages = {10071-10080},
doi = {http://doi.org/10.1002/chem.201101220}
}
Spin switching and intelligent contrast agents in MRT.
R. Herges, Nachr. Chem. 2011, 59, 817-821.
Abstract:
Isolierte Atome und Moleküle existieren in zwei magnetischen Zuständen: dia- und para magnetisch. Bis vor kurzem war magnetische Bistabilität auf Festkörper beschränkt und Einzelmoleküle ließen sich bei Raumtemperatur nicht zwischen diesen Zuständen hin und her schalten. Die Entwicklung des ligandgetriebenen Spinwechsels erlaubt nun auch das Spinschalten ohne kooperative Effekte. Neue Anwendungen wie schaltbare Kontrastmittel für die Kernspintomographie sind so möglich.
BibTeX:
@article{Herges2011,
author = {Herges, Rainer.},
title = {Spin switching and intelligent contrast agents in MRT.},
journal = {Nachr. Chem.},
year = {2011},
volume = {59},
number = { },
pages = {817-821},
doi = {http://doi.org/10.1002/nadc.201190013}
}
Azobenzene-Containing Triazatriangulenium Adlayers on Au(111): Structural and Spectroscopic Characterization.
U. Jung, S. Kuhn, U. Cornelissen, F. Tuczek, T. Strunskus, V. Zaporojtchenko, J. Kubitschke, R. Herges and O. Magnussen, Langmuir 2011, 27, 5899-5908.
Abstract:
Adlayers of different azobenzene-functionalized derivs. of the triazatriangulenium (TATA) platform on Au(111) surfaces were studied by scanning tunneling microscopy (STM), x-ray photoelectron scpectroscopy (XPS), gap-mode surface-enhanced Raman spectroscopy (gap-mode SERS), and cyclic voltammetry (CV). The chem. compn. of the adlayers is in good agreement with the mol. structure, i.e., different chem. groups attached to the azobenzene functionality were identified. Also, the presence of the azobenzene moieties in the adlayers was verified by the vibration spectra and electrochem. data. The mols. remain intact upon adsorption with the freestanding functional groups oriented perpendicularly to the TATA platform and thus also to the substrate surface.
BibTeX:
@article{Jung2011,
author = {Jung, Ulrich and Kuhn, Sonja and Cornelissen, Ursula and Tuczek, Felix and Strunskus, Thomas and Zaporojtchenko, Vladimir and Kubitschke, Jens and Herges, Rainer and Magnussen, Olaf.},
title = {Azobenzene-Containing Triazatriangulenium Adlayers on Au(111): Structural and Spectroscopic Characterization.},
journal = {Langmuir},
year = {2011},
volume = {27},
number = { },
pages = {5899-5908},
doi = {http://doi.org/10.1021/la104654p}
}
Adlayers based on molecular platforms of trioxatriangulenium.
S. Kuhn, U. Jung, S. Ulrich, R. Herges and O. Magnussen, Chem. Commun. 2011, 47, 8880-8882.
Abstract:
The platform approach for prepn. of mol. adlayers with freestanding functional groups was extended to systems from the trioxatriangulenium ion. Self-assembled monolayers of these compds. were prepd. on Au(111) surfaces and characterized by scanning tunneling microscopy, revealing highly-ordered structures.
BibTeX:
@article{Kuhn2011,
author = {Kuhn, Sonja and Jung, Ulrich and Ulrich, Sandra and Herges, Rainer and Magnussen, Olaf.},
title = {Adlayers based on molecular platforms of trioxatriangulenium.},
journal = {Chem. Commun.},
year = {2011},
volume = {47},
number = { },
pages = {8880-8882},
doi = {http://doi.org/10.1039/C1CC12598B}
}
Coarctate versus Pericyclic Reactivity in Naphthalene-Fused Azo-Ene-Ynes: Synthesis of Benzocinnolines and Benzoisoindazoles.
S.P. McClintock, L.N. Zakharov, R. Herges and M.M. Haley, Chem. Eur. J. 2011, 17, 6798-6806.
Abstract:
The cyclization reactions of naphthalene-fused azo-ene-yne compds. are explored both computationally and exptl. Calcns. reveal that naphtho-fusion to an azo-ene-yne scaffold does not significantly alter the transition state energies compared to the benzene-based systems; however, fusing the naphthalene in an angular fashion leads to lower energy intermediates due to the creation of arenes possessing greater aromaticity. Exptl., the cyclization of the angular systems yields not only the expected monomeric benzocinnolines and benzoisoindazoles, but also several dimeric structures, including one that readily isomerizes in the presence of light and/or trace acid.
BibTeX:
@article{McClintock2011,
author = {McClintock, Sean P. and Zakharov, Lev N. and Herges, Rainer and Haley, Michael M.},
title = {Coarctate versus Pericyclic Reactivity in Naphthalene-Fused Azo-Ene-Ynes: Synthesis of Benzocinnolines and Benzoisoindazoles.},
journal = {Chem. Eur. J.},
year = {2011},
volume = {17},
pages = {6798-6806},
doi = {http://doi.org/10.1002/chem.201002936}
}
Stability and Aromaticity of Charged Mobius[4n]Annulenes.
E.-K. Mucke, B. Schoenborn, F. Koehler and R. Herges, J. Org. Chem. 2011, 76, 35-41.
Abstract:
A no. of parent arom. Mobius annulenes that violate the Hueckel rule were proposed theor. Unfortunately, these species are thermodynamically and kinetically unstable and probably impossible to synthesize. The authors therefore systematically screened a large no. of annulene anions, dianions, and dications and predict that a Mobius [14]annulene dication is not only the most stable isomer among these monocyclic structures but also the global min. on the (CH)142+ hypersurface including bicyclic and tricyclic isomers. Thus, under stable ion conditions the Mobius[14]annulene dication should be stable toward cis-trans isomerizations and electrocyclic reactions which are the most probable pathways limiting the lifetime of Mobius annulenes.
BibTeX:
@article{Mucke2011,
author = {Mucke, Eva-Katrin and Schoenborn, Boyke and Koehler, Felix and Herges, Rainer.},
title = {Stability and Aromaticity of Charged Mobius[4n]Annulenes.},
journal = {J. Org. Chem.},
year = {2011},
volume = {76},
number = { },
pages = {35-41},
doi = {http://doi.org/10.1021/jo100798e}
}
In situ atomic force microscopy studies of reversible light-induced switching of surface roughness and adhesion in azobenzene-containing PMMA films.
M. Mueller, Y. Gonzalez-Garcia, C. Pakula, V. Zaporojtchenko, T. Strunskus, F. Faupel, R. Herges, D. Zargarani and O.M. Magnussen, Appl. Surf. Sci. 2011, 257, 7719-7726.
Abstract:
Thin films in the range 40-80 nm of a blend of PMMA with an azobenzene deriv. were studied directly during UV and blue light irradn. by at. force microscopy (AFM), revealing highly reversible changes in the surface roughness and the film adhesion. UV light induces an ≈80% increase in surface roughness, whereas illumination by blue light completely reverses these changes. Based on the obsd. surface topog. and transition kinetics a reversible mass flow mechanisms is suggested, where the polarity changes upon switching trigger a wetting-dewetting transition in a surface segregation layer of the chromophore. Similar AFM measurements of the pull-off force indicate a decrease upon UV and an increase after blue light illumination with a complex kinetic behavior: a rapid initial change, attributed to the change in the cis isomer fraction of the azobenzene deriv., and a more gradual change, indicative of slow structural reorganization.
BibTeX:
@article{Mueller2011,
author = {Mueller, M. and Gonzalez-Garcia, Y. and Pakula, C. and Zaporojtchenko, V. and Strunskus, T. and Faupel, F. and Herges, R. and Zargarani, D. and Magnussen, O. M.},
title = {In situ atomic force microscopy studies of reversible light-induced switching of surface roughness and adhesion in azobenzene-containing PMMA films.},
journal = {Appl. Surf. Sci.},
year = {2011},
volume = {257},
number = { },
pages = {7719-7726},
doi = {http://doi.org/10.1016/j.apsusc.2011.04.016}
}
Optical switching behavior of azobenzene/PMMA blends with high chromophore concentration
C. Pakula, C. Hanisch, V. Zaporojtchenko, T. Strunskus, C. Bornholdt, D. Zargarani, R. Herges and F. Faupel, J. Mater. Sci. 2011, 46, 2488-2494.
Abstract:
In this article, the authors will present a simple way to produce thin solid organic films, with a content of more than 60 wt% photoactive molecules dispersed in a polymeric matrix showing an almost complete and fully reversible photoisomerization. These high filling factors could be achieved by using branched side chains in the molecules, which prevent crystallization. The chromophores were codissolved with the polymer Polymethylmethacrylate (PMMA) of different Mw in toluene in various concentrations and spin casted onto the substrate. The effect of the Mw of PMMA on the switching kinetics and the agglomeration tendency of different molecule configurations were investigated.
BibTeX:
@article{Pakula2010a,
author = {Pakula, Christina and Hanisch, Christian and Zaporojtchenko, Vladimir and Strunskus, Thomas and Bornholdt, Claudia and Zargarani, Dordaneh and Herges, Rainer and Faupel, Franz},
title = {Optical switching behavior of azobenzene/PMMA blends with high chromophore concentration},
journal = {J. Mater. Sci.},
year = {2011},
volume = {46},
pages = {2488-2494},
doi = {http://doi.org/10.1007/s10853-010-5097-9}
}
The First Porous MOF with Photoswitchable Linker Molecules
A. Modrow, D. Zargarani, R. Herges and N. Stock, J. Chem. Soc. Dalton Trans. 2011, 40, 4217-4222.
Abstract:
We synthesized a porous twofold interpenetrated MOF [Zn2(NDC)2(1)] (coined CAU-5) using 3-azo-phenyl-4,4′-bipyridine (1), 2,6-naphthalenedicarboxylic acid, and Zn(NO3)2·6H2O. The azo-functionality protrudes into the pores, and can be switched, by irradiation with UV light (365 nm), from the thermodynamically stable trans-isomer to the cis-isomer. Back-switching was achieved thermally and with an irradiation wavelength of λmax = 440 nm.
BibTeX:
@article{Reher2011,
author = {Modrow, Antje and Zargarani, Dordaneh and Herges, Rainer and Stock, Norbert},
title = {The First Porous MOF with Photoswitchable Linker Molecules},
journal = {J. Chem. Soc. Dalton Trans.},
year = {2011},
volume = {40},
pages = {4217-4222},
doi = {http://doi.org/10.1039/C0DT01629B}
}
Light-induced Spin-Change by Photodissociable External Ligands: A New Principle for Magnetic Switching of Molecules.
S. Thies, H. Sell, C. Schuett, C. Bornholdt, C. Naether, F. Tuczek and R. Herges, J. Am. Chem. Soc. 2011, 133, 16243-16250.
Abstract:
Magnetic bistability in spin crossover materials generally is a collective phenomenon which arises from the cooperative interaction of a large no. of microscopic magnetic moments within the crystal lattice in the solid state. We now report on individual mols. in homogeneous soln. that are switched between the dia- and paramagnetic state at room temp. by light driven coordination induced spin state switching (LD-CISSS). Switching of the coordination no. (and concurrently of the spin state) is achieved by using Ni-porphyrin as a square planar platform, and azopyridines as photodissociable axial ligands. The square planar Ni-porphyrin is diamagnetic (low spin, S=0), and all complexes with axial ligands are paramagnetic (high spin, S=1). Assocn. consts. are detd. for all conceivable 1:1 and 1:2 porphyrin/azopyridine complexes. The binding consts. of the trans azopyridines are larger than those of the corresponding cis isomers. Thus, upon irradn. with UV light (365 nm, trans → cis), and visible light (455 nm, cis → trans) switching of magnetic properties is achieved. Upon substitution of the azopyridines in 4,4'-position with larger substituents the difference in trans and cis assocn. consts., and thus the switching efficiency is increased. A photoinduced switching between 20 and 68 % paramagnetic Ni species in soln. is achieved with iso-Pr substituents at room temp.
BibTeX:
@article{Thies2011,
author = {Thies, Steffen and Sell, Hanno and Schuett, Christian and Bornholdt, Claudia and Naether, Christian and Tuczek, Felix and Herges, Rainer.},
title = {Light-induced Spin-Change by Photodissociable External Ligands: A New Principle for Magnetic Switching of Molecules.},
journal = {J. Am. Chem. Soc.},
year = {2011},
volume = {133},
number = { },
pages = {16243-16250},
doi = {http://doi.org/10.1021/ja206812f}
}
5-Chloro-2-(phenyldiazenyl)pyridine.
S. Thies, C. Naether and R. Herges, Acta Crystallogr., Sect. E: Struct. Rep. Online 2011, 67, o3298.
Abstract:
In 5-chloro-2-(phenyldiazenyl)pyridine, C11H8ClN3, the azo group adopts a trans conformation and the dihedral angle between the 6-membered rings is 15.47(8)°. Crystallog. data are given.
BibTeX:
@article{Thies2011a,
author = {Thies, Steffen and Naether, Christian and Herges, Rainer.},
title = {5-Chloro-2-(phenyldiazenyl)pyridine.},
journal = {Acta Crystallogr., Sect. E: Struct. Rep. Online},
year = {2011},
volume = {67},
number = { },
pages = {o3298},
doi = {http://doi.org/10.1107/S1600536811047556}
}
Magnetic Bistability of Molecules in Homogeneous Solution at Room Temperature
S. Venkataramani, U. Jana, M. Dommaschk, F.D. Sönnichsen, F. Tuczek and R. Herges, Science 2011, 331, 445-448.
Abstract:
Magnetic bistability, as manifested in the magnetization of ferromagnetic materials or spin crossover in transition metal complexes, has essentially been restricted to either bulk materials or to very low temperatures. We now present a molecular spin switch that is bistable at room temperature in homogeneous solution. Irradiation of a carefully designed nickel complex with blue-green light (500 nanometers) induces coordination of a tethered pyridine ligand and concomitant electronic rearrangement from a diamagnetic to a paramagnetic state in up to 75% of the ensemble. The process is fully reversible on irradiation with violet-blue light (435 nanometers). No fatigue or degradation is observed after several thousand cycles at room temperature under air. Preliminary data show promise for applications in magnetic resonance imaging.
BibTeX:
@article{Venkataramani2011,
author = {Venkataramani, Sugumar and Jana, Umasish and Dommaschk, Marcel and Sönnichsen, Frank D. and Tuczek, Felix and Herges, Rainer},
title = {Magnetic Bistability of Molecules in Homogeneous Solution at Room Temperature},
journal = {Science},
year = {2011},
volume = {331},
pages = {445-448},
doi = {http://doi.org/10.1126/science.1201180}
}
Phenanthrene-Fused Azo-ene-ynes: Synthesis of Dibenzo[f,h]cinnoline and Dibenzo[e,g]isoindazole Derivatives.
B.S. Young, F. Kohler, R. Herges and M.M. Haley, J. Org. Chem. 2011, 76, 8483-8487.
Abstract:
The cyclization reactions of a phenanthreno-fused azo-ene-yne compd. have been studied both exptl. and computationally. Exptl. results show that this system is prone to dimerization, more so than previously studied naphthalene- and benzene-based analogs. Calcns. reveal that pyrazoles and arene-fused pyrazoles strongly stabilize carbenes in the 5-position through "coarctate conjugation", suggesting a stationary concn. of the carbenes/carbenoids during cyclization that is high enough for dimerization.
BibTeX:
@article{Young2011,
author = {Young, Brian S. and Kohler, Felix and Herges, Rainer and Haley, Michael M.},
title = {Phenanthrene-Fused Azo-ene-ynes: Synthesis of Dibenzo[f,h]cinnoline and Dibenzo[e,g]isoindazole Derivatives.},
journal = {J. Org. Chem.},
year = {2011},
volume = {76},
number = { },
pages = {8483-8487},
doi = {http://doi.org/10.1021/jo201378t}
}
Reversible light-induced capacitance switching of azobenzene ether/PMMA blends
V. Zaporojtchenko, C. Pakula, S. Wahyuni Basuki, T. Strunskus, D. Zargarani, R. Herges and F. Faupel, Appl. Phys. A 2011, 102, 421-427.
Abstract:
Fully reversible light-induced switching of the capacitance with changes larger than 50% has been achieved by using photo-active thin polymer films. The films consist of PMMA polymer blended with high concentrations of branched azobenzene ether dye molecules. Polymer thin sheet capacitors can be easily produced by spin coating and drop casting in various thicknesses ranging from 100 nm to 8 µm, respectively. Reversible capacitance switching is induced by illumination with UV and visible light, respectively. The capacitance change is correlated to the trans to cis isomerization of the azobenzene ether molecules and the alignment of the molecular dipoles in the film. Switching times depend on chromophore concentration, film thickness and light intensity used. The influence of wavelength of the light, of the temperature as well as of an electrical field applied during illumination on the capacitance change is addressed.
BibTeX:
@article{Zaporojtchenko2011,
author = {Zaporojtchenko, Vladimir and Pakula, Christina and Wahyuni Basuki, Sri and Strunskus, Thomas and Zargarani, Dordaneh and Herges, Rainer and Faupel, Franz},
title = {Reversible light-induced capacitance switching of azobenzene ether/PMMA blends},
journal = {Appl. Phys. A},
year = {2011},
volume = {102},
pages = {421-427},
doi = {http://doi.org/10.1007/s00339-010-6139-5}
}
Synthesis and properties of di- and trinitrobenzyl substituted pyridine derivates.
A. Frej, C. Goeschen, C. Näther, U. Lüning and R. Herges, J. Phys. Org. Chem. 2010, 23, 1093-1098.
Abstract:
A new method to obtain di- and trinitrobenzyl substituted pyridines is presented. By systematic variation of reaction parameters the reaction conditions were optimized. The novel synthesis circumvents the commonly used nitration of benzyl pyridines, and thus avoids the nitration of the heterocycle which is a common side reaction. Furthermore, the starting materials for the synthesis of a variety of photochromic nitrobenzyl pyridines are easily accessible. The halflifes of the phototautomers of several new di- and trinitrobenzyl-substituted pyridines were determined.
BibTeX:
@article{Frej2010,
author = {Adrian Frej and Catrin Goeschen and Christian Näther and Ulrich Lüning and Rainer Herges},
title = {Synthesis and properties of di- and trinitrobenzyl substituted pyridine derivates.},
journal = {J. Phys. Org. Chem.},
year = {2010},
volume = {23},
pages = {1093-1098},
doi = {http://doi.org/10.1002/poc.1781}
}
Photoswitching of azobenzene multilayers on a layered semiconductor
J. Iwicki, E. Ludwig, M. Kalläne, J. Buck, F. Köhler, R. Herges, L. Kipp and K. Roßnagel, Applied Physics Letters 2010, 97, 063112.
Abstract:
In situ photoelectron spectroscopy is used to study the adsorption and photoisomerization of azobenzene multilayers on the layered semiconductor HfS2 at liquid nitrogen temperatures. The measured valence band spectra indicate weak molecule–substrate coupling and provide evidence for reversible switching of azobenzene multilayers by light with different wavelengths. The photoswitching manifests itself in spectral shifts due to changes in the electrical surface conductance and in modifications of the electronic structure consistent with the results of outer valence Green’s function calculations. The photoemission results appear to establish azobenzene as an optoelectrical molecular switch.
BibTeX:
@article{Iwicki2010,
author = {Iwicki, Jaroslaw and Ludwig, E. and Kalläne, M. and Buck, J. and Köhler, Felix and Herges, Rainer and Kipp, Lutz and Roßnagel, Kai},
title = {Photoswitching of azobenzene multilayers on a layered semiconductor},
journal = {Applied Physics Letters},
year = {2010},
volume = {97},
pages = {063112},
doi = {http://doi.org/10.1063/1.3479502}
}
Photoswitching Behavior of Azobenzene-Containing Alkanethiol Self-Assembled Monolayers on Au Surfaces
U. Jung, O. Filinova, S. Kuhn, D. Zargarani, C. Bornholdt, R. Herges and O. Magnussen, Langmuir 2010, 26, 13913-13923.
Abstract:
The photoisomerization of self-assembled monolayers of azobenzene-containing alkanethiols, as well as of mixed monolayers of these substances with n-alkanethiol spacer molecules on Au surfaces, was studied by photoelectrochemical measurements and surface plasmon resonance spectroscopy. A strong dependence on the molecular structure of the adsorbates was found, specifically on the linker between the azobenzene moiety and the alkanethiol: while molecules with an amide group were photoinactive, those with an ether group exhibited pronounced, reversible photoisomerization in pure and mixed adlayers. Both trans−cis and cis−trans isomerization followed first-order kinetics with time constants that suggest high quantum efficiencies for these processes.
BibTeX:
@article{Jung2010,
author = {Jung, Ulrich and Filinova, Olena and Kuhn, Sonja and Zargarani, Dordaneh and Bornholdt, Claudia and Herges, Rainer and Magnussen, Olaf},
title = {Photoswitching Behavior of Azobenzene-Containing Alkanethiol Self-Assembled Monolayers on Au Surfaces},
journal = {Langmuir},
year = {2010},
volume = {26},
pages = {13913-13923},
doi = {http://doi.org/10.1021/la1015109}
}
Synthesis of Functionalized Triazatriangulenes for Application in Photo-switchable Self-assembled Monolayers
J. Kubitschke, C. Näther and R. Herges, Eur. J. Org. Chem. 2010, 5041-5055.
Abstract:
Various triazatriangulenes are synthesized by nucleophilic attack at the central C atom of triazatriangulenium ions. The molecular functions, especially azobenzenes, are fixed via an ethynyl linker by in situ deprotection of trimethylsilyl alkynes. The structure of two of these molecules is further investigated by X-ray crystallography.
The photo-induced trans/cis-isomerization of the azobenzene substituted derivatives is analyzed in solution and shows great promise for the preparation of switchable functionalized monolayers, as the triazatriangulenes are known for their self-assembly on gold surfaces.
BibTeX:
@article{Kubitschke2010,
author = {Kubitschke, Jens and Näther, Christian and Herges, Rainer},
title = {Synthesis of Functionalized Triazatriangulenes for Application in Photo-switchable Self-assembled Monolayers},
journal = {Eur. J. Org. Chem.},
year = {2010},
pages = {5041-5055},
doi = {http://doi.org/10.1002/ejoc.201000650}
}
Self-assembly of triazatriangulenium-based functional adlayers on Au(111) surfaces.
S. Kuhn, B. Baisch, U. Jung, T. Johannsen, J. Kubitschke, R. Herges and O. Magnussen, Phys. Chem. Chem. Phys. 2010, 12, 4481-4487.
Abstract:
Detailed scanning tunneling microscopy studies of the attachment of freestanding mol. functions to Au(111) surfaces via self-assembly of functional mols. based on triazatriangulenium platforms are presented. As shown for mols. with side chains of different length and Ph, azobenzyl, or azobenzyl derivs. with different terminal groups (iodo, cyano, or dimethyl) as functional units, this approach allows the prepn. of very stable, hexagonally ordered adlayers. The intermol. spacings in these adlayers are independent of the attached functions with the latter being orientated perpendicular to the Au surface. Due to their open structure, adlayers of platforms with attached functional groups exhibit a tendency towards bilayer formation, which can be suppressed by derivatization with appropriate terminal groups.
BibTeX:
@article{Kuhn2010,
author = {Kuhn, Sonja and Baisch, Belinda and Jung, Ulrich and Johannsen, Torben and Kubitschke, Jens and Herges, Rainer and Magnussen, Olaf.},
title = {Self-assembly of triazatriangulenium-based functional adlayers on Au(111) surfaces.},
journal = {Phys. Chem. Chem. Phys.},
year = {2010},
volume = {12},
number = { },
pages = {4481-4487},
doi = {http://doi.org/10.1039/b922882a}
}
27- to 39-Membered Pyridine Macrocycles
U. Lüning, E. Mak, M. Zindler, B. Hartkopf and R. Herges, Eur. J. Org. Chem. 2010, 4932-4940.
Abstract:
Abstract: A set of 27- to 39-membered pyridine macrocycles 2 and 3 has been synthesized by Williamson ether synthesis or ring closing metathesis. The pyridines are 2,6-disubstituted to allow endo-interactions. In addition to the length, also the nature of an aliphatic chain has been varied: saturated (2) and unsaturated (3).
BibTeX:
@article{Luening2010,
author = {Lüning, Ulrich and Mak, Ellen and Zindler, Melanie and Hartkopf, Britta and Herges, Rainer},
title = {27- to 39-Membered Pyridine Macrocycles},
journal = {Eur. J. Org. Chem.},
year = {2010},
pages = {4932-4940},
doi = {http://doi.org/10.1002/ejoc.201000505}
}
Single azopyridine-substituted porphyrin molecules for configurational and electronic switching
F. Matino, G. Schull, U. Jana, F. Köhler, R. Berndt and R. Herges, Chem. Comm. 2010, 6780-6782.
Abstract:
A new azopyridine functionalized Ni–porphyrin was synthesized as a model compound for deposition and switch on surfaces. Two geometrically and electronically different states of single molecules on Au(111) were found by scanning tunneling microscopy/spectroscopy and analyzed with density functional calculations.
BibTeX:
@article{Matino2010,
author = {Matino, Francesca and Schull, Guillaume and Jana, Umasish and Köhler, Felix and Berndt, Richard and Herges, Rainer},
title = {Single azopyridine-substituted porphyrin molecules for configurational and electronic switching},
journal = {Chem. Comm.},
year = {2010},
pages = {6780-6782},
doi = {http://doi.org/10.1039/C0CC00959H}
}
Singly and Doubly Twisted [36]Annulenes: Synthesis and Calculations.
A.R. Mohebbi, E.-K. Mucke, G.R. Schaller, F. Koehler, F.D. Soennichsen, L. Ernst, C. Naether and R. Herges, Chem. Eur. J. 2010, 16, 7767-7772.
Abstract:
A cyclophane with a [36]annulene periphery, including four anthrylene and two phenylene units (I), was synthesized in a four-step sequence using a McMurry cyclization. Upon crystn. from different solvents, four different conformations were detd. by X-ray structure anal. Two conformations exhibit a double twist (Hueckel topol.) and two structures include a single twist (Moebius topol.). By using DFT calcns. a conformation with a triple twist (Moebius) was located. However, our calcns. and the NMR spectroscopy data do not provide evidence for aromaticity (for Moebius structures) or antiaromaticity (for Hueckel structures).
BibTeX:
@article{Mohebbi2010,
author = {Mohebbi, Ali Reza and Mucke, Eva-Katrin and Schaller, Gaston R. and Koehler, Felix and Soennichsen, Frank D. and Ernst, Ludger and Naether, Christian and Herges, Rainer.},
title = {Singly and Doubly Twisted [36]Annulenes: Synthesis and Calculations.},
journal = {Chem. Eur. J.},
year = {2010},
volume = {16},
number = { },
pages = {7767-7772}
}
The [13]Annulene Cation Is a Stable Moebius Annulene Cation.
E.-K. Mucke, F. Koehler and R. Herges, Org. Lett. 2010, 12, 1708-1711.
Abstract:
The isomers of the [n]annulene cation series (n = 13, 17, and 21) were systematically scrutinized by DFT, SCS-MP2, and coupled-cluster methods. Only in the case of the [13]annulene cation the global min. is clearly a Mobius structure. According to our theor. predictions, the [13]annulene cation should also be kinetically stable. Thus, the [13]annulene cation is the most promising candidate for the synthesis of a parent Moebius arom. system among the neutral and cationic annulenes.
BibTeX:
@article{Mucke2010,
author = {Mucke, Eva-Katrin and Koehler, Felix and Herges, Rainer.},
title = {The [13]Annulene Cation Is a Stable Moebius Annulene Cation.},
journal = {Org. Lett.},
year = {2010},
volume = {12},
number = { },
pages = {1708-1711},
doi = {http://doi.org/10.1021/ol1002384}
}
Reversible light-controlled conductance switching of azobenzene-based metal/polymer nanocomposites.
C. Pakula, V. Zaporojtchenko, T. Strunskus, D. Zargarani, R. Herges and F. Faupel, Nanotechnology 2010, 21, 465201/1-465201/6.
Abstract:
We present a new concept of light-controlled conductance switching based on metal/polymer nanocomposites with dissolved chromophores that do not have intrinsic current switching ability. Photoswitchable metal/PMMA nanocomposites were prepd. by phys. vapor deposition of Au and Pt clusters, resp., onto spin-coated thin poly(methylmethacrylate) films doped with azo-dye mols. High dye concns. were achieved by functionalizing the azo groups with tails and branches, thus enhancing soly. The composites show completely reversible optical switching of the absorption bands upon alternating irradn. with UV and blue light. We also demonstrate reversible light-controlled conductance switching. This is attributed to changes in the metal cluster sepn. upon isomerization based on model expts. where analogous conductance changes were induced by swelling of the composite films in org. vapors and by tensile stress.
BibTeX:
@article{Pakula2010,
author = {Pakula, Christina and Zaporojtchenko, Vladimir and Strunskus, Thomas and Zargarani, Dordaneh and Herges, Rainer and Faupel, Franz.},
title = {Reversible light-controlled conductance switching of azobenzene-based metal/polymer nanocomposites.},
journal = {Nanotechnology},
year = {2010},
volume = {21},
number = { },
pages = {465201/1-465201/6},
doi = {http://doi.org/10.1088/0957-4484/21/46/465201}
}
Novel loop-like aromatic compounds: a further step on the road to nanobelts and nanotubes.
V. Rajuri, D. Ajami, G.R. Schaller, C. Naether and R. Herges, Beilstein J. Org. Chem. 2010, 6, No. 30.
Abstract:
The synthesis and crystal structural characterization of new compds. 2-6 were accomplished. As a common synthetic methodol., the Diels-Alder reaction was applied to 9,9',10,10'-tetradehydrodianthracene (TDDA) (7) to furnish the annulenes 2 and 3, annulene 6 and adduct 5.
BibTeX:
@article{Rajuri2010,
author = {Rajuri, Venkataramana and Ajami, Dariush and Schaller, Gaston R. and Naether, Christian and Herges, Rainer.},
title = {Novel loop-like aromatic compounds: a further step on the road to nanobelts and nanotubes.},
journal = {Beilstein J. Org. Chem.},
year = {2010},
volume = {6},
number = { },
pages = {No. 30},
doi = {http://doi.org/10.3762/bjoc.6.30}
}
Ion Transport Across Membranes Facilitated by a Dynamic Combinatorial Library.
V. Saggiomo, C. Goeschen, R. Herges, R. Quesada and U. Luening, Eur. J. Org. Chem. 2010, 2337-2343.
Abstract:
A dynamic combinatorial library (DCL) consisting of dialdehydes and diamines has been used to facilitate the transport of calcium ions across a supported liq. membrane (SLM). In a dual selection process, the calcium ions first select matching macrocycles 3 or 5 from the DCL. Then only one of the macrocycle-calcium complexes (5·Ca2+) efficiently transports the calcium ions due to its better balance between lipo- and hydrophilicity. The special setup of a DCL combined with an SLM directly finds suitable carriers for ion transport starting from diamine and dialdehyde building blocks 1, 2 and 4. The synthesis of the new, more lipophilic 4-pentoxypyridine-2,6-dicarbaldehyde (4) is also described, and the first transport expts. with liposomes are discussed.
BibTeX:
@article{Saggiomo2010,
author = {Saggiomo, Vittorio and Goeschen, Catrin and Herges, Rainer and Quesada, Roberto and Luening, Ulrich.},
title = {Ion Transport Across Membranes Facilitated by a Dynamic Combinatorial Library.},
journal = {Eur. J. Org. Chem.},
year = {2010},
number = { },
pages = {2337-2343},
doi = {http://doi.org/10.1002/ejoc.201000038}
}
Coordination-Induced Spin Crossover (CISCO) through Axial Bonding of Substituted Pyridines to Nickel-Porphyrins: sigma-Donor vs pi-Acceptor Effects
S. Thies, C. Bornholdt, F. Köhler, F.D. Sönnichsen, C. Näther, F. Tuczek and R. Herges, Chem. Eur. J. 2010, 16, 10074-10083.
Abstract:
Ni-porphyrins with their rigid quadratic planar coordination framework provide an excellent model to study the coordination-induced spincrossover (CISCO) effect because bonding of one or two axial ligands to the metal center leads to a spin transition from S = 0 to S = 1. Herein both equilibrium constants K1S and K2, and for the first time also the corresponding thermodynamic parameters ΔH1S, ΔH2, ΔS1S, and ΔS2 are determined for the reaction of a nickel-porphyrin (Ni-tetrakis(pentafluorophenyl)porphyrin) with different 4-substituted pyridines by temperature dependent NMR spectroscopy. The association constants K1S and K2 are correlated with the basicity of the 4-substituted pyridines (R: OMe > H > CO2Et > NO2) whereas the ΔH1S values exhibit a completely different order (OMe < H > CO2Et > NO2). 4-nitropyridine exhibits the largest binding enthalpy which, however, is overcompensated by a large negative binding entropy. We attribute the large association enthalpy of nitropyridine with porphyrin to the back donation of electrons from the Ni dxz and dyz orbitals into the π∗ orbitals of pyridine and the negative association entropy to a decrease in vibrational and internal rotation entropy of the more rigid porphyrin-pyridine complex. Back donation for the nitro- and cyano-pyridine complexes is also confirmed by IR spectroscopy, showing a shift of the N-O and C-N vibrations, respectively, to lower wave numbers. X-ray structures of 2:1 complexes with nitro-, cyano- and dimethylaminopyridine provide further indication of a back donation. A further trend has been observed. The more basic the pyridine the larger is K1S relative to K2. For nitropyridine K2 is 17 times larger than K1S and in case of methoxypyridine K2 and K1S are almost equal.
BibTeX:
@article{Thies2010,
author = {Thies, Steffen and Bornholdt, Claudia and Köhler, Felix and Sönnichsen, Frank D. and Näther, Christian and Tuczek, Felix and Herges, Rainer},
title = {Coordination-Induced Spin Crossover (CISCO) through Axial Bonding of Substituted Pyridines to Nickel-Porphyrins: sigma-Donor vs pi-Acceptor Effects},
journal = {Chem. Eur. J.},
year = {2010},
volume = {16},
pages = {10074-10083}
}
Switching Single Azopyridine Supramolecules in Ordered Arrays on Au(111).
Y. Wang, X. Ge, G. Schull, R. Berndt, H. Tang, C. Bornholdt, F. Koehler and R. Herges, J. Am. Chem. Soc. 2010, 132, 1196-1197.
Abstract:
4,4-Azopyridine trimers and 4-phenylazopyridine dimers were reversibly switched in ordered arrays on Au(111). During the switching process, single weak C-H. N hydrogen bonds are broken and reformed.
BibTeX:
@article{Wang2010,
author = {Wang, Yongfeng and Ge, Xin and Schull, Guillaume and Berndt, Richard and Tang, Hao and Bornholdt, Claudia and Koehler, Felix and Herges, Rainer},
title = {Switching Single Azopyridine Supramolecules in Ordered Arrays on Au(111).},
journal = {J. Am. Chem. Soc.},
year = {2010},
volume = {132},
pages = {1196-1197},
doi = {http://doi.org/10.1021/ja9080277}
}
Mounting Freestanding Molecular Functions onto Surfaces: The Platform Approach.
B. Baisch, D. Raffa, U. Jung, O.M. Magnussen, C. Nicolas, J. Lacour, J. Kubitschke and R. Herges, J. Am. Chem. Soc. 2009, 131, 442-443.
Abstract:
A modular system has been developed to mount mols. upright onto metal surfaces in a well controlled geometry. The approach is based on a reactive platform (triazatriangulenium salt) with an electrophilic center. Functional mols. are attached via C-C bond formation. The distance from the surface can be varied by a spacer, and the distance of the functional units from each other by the size of the platform. Self-assembly of the parent triazaangulenium salt as well as the functionalized platforms on Au(111) surfaces results in stable, hexagonally ordered adlayers.
BibTeX:
@article{Baisch2009,
author = {Baisch, Belinda and Raffa, Diego and Jung, Ulrich and Magnussen, Olaf M. and Nicolas, Cyril and Lacour, Jerome and Kubitschke, Jens and Herges, Rainer.},
title = {Mounting Freestanding Molecular Functions onto Surfaces: The Platform Approach.},
journal = {J. Am. Chem. Soc.},
year = {2009},
volume = {131},
pages = {442-443},
doi = {http://doi.org/10.1021/ja807923f}
}
Is the [9]Annulene Cation a Moebius Annulene?.
G. Bucher, S. Grimme, R. Huenerbein, A.A. Auer, E. Mucke, F. Koehler, J. Siegwarth and R. Herges, Angew. Chem., Int. Ed. 2009, 48, 9971-9974, S9971/1-S9971/12.
Abstract:
Does it do the twist? High-level theoretical calculations show that the [9]annulene cation exists in two isomers: a twisted 4n electron Möbius aromatic compound, and a non-twisted boat-like Hückel conformation (see scheme). The latter form was detected by laser flash photolysis experiments; an example of a stable, charged, or uncharged parent Möbius annulene is still elusive.
BibTeX:
@article{Bucher2009,
author = {Bucher, Goetz and Grimme, Stefan and Huenerbein, Robert and Auer, Alexander A. and Mucke, Eva and Koehler, Felix and Siegwarth, Jan and Herges, Rainer},
title = {Is the [9]Annulene Cation a Moebius Annulene?.},
journal = {Angew. Chem., Int. Ed.},
year = {2009},
volume = {48},
pages = {9971-9974, S9971/1-S9971/12},
doi = {http://doi.org/10.1002/anie.200900886}
}
Substituent effects on 61Ni NMR chemical shifts.
M. Buehl, D. Peters and R. Herges, Dalton Trans. 2009, 6037-6044.
Abstract:
61Ni chem. shifts of Ni(all-trans-cdt)L (cdt = cyclododecatriene, L = none, CO, PMe3), Ni(CO)4, Ni(C2H4)2(PMe3), Ni(cod)2 (cod = cyclooctadiene) and Ni(PX3)4 (X = Me, F, Cl) are computed at the GIAO (gauge-including AOs), BPW91, B3LYP and BHandHLYP levels, using BP86-optimized geometries and an indirect referencing scheme. For this set of compds., substituent effects on δ(61Ni) are better described with hybrid functionals than with the pure BPW91 functional. On going from Ni(all-trans-cdt) to Ni(all-cis-cdt) the computations predict substantial shielding of the 61Ni nucleus by nearly 700 ppm, as well as a sharp increase of the elec. field gradient at this position. The latter result is predicted to afford an undetectably broad 61Ni NMR line for the all-cis-cdt complex, rationalizing the apparent failure to record the NMR spectrum exptl.
BibTeX:
@article{Buehl2009,
author = {Buehl, Michael and Peters, Dietmund and Herges, Rainer},
title = {Substituent effects on 61Ni NMR chemical shifts.},
journal = {Dalton Trans.},
year = {2009},
pages = {6037-6044},
doi = {http://doi.org/10.1039/b902308a}
}
Thioamidation of Single-Walled Carbon Nanotubes: a New Chemical Functionalization Protocol by the Willgerodt-Kindler Reaction.
H.R. Darabi, S. Mohandessi, K. Aghapoor, F. Mohsenzadeh, M.H. Karouei, F. Tahoori and R. Herges, Aust. J. Chem. 2009, 62, 413-418.
Abstract:
A new and convenient method for covalent attachment of thioamide groups to the side-walls of carbon nanotubes (SWNT) via the Willgerodt-Kindler (WK) reaction is presented. Treating SWNTs with 4-acetylaniline and subsequently with morpholine as a secondary amine and sulfur leads to the thioamidation of SWNTs. This approach paves the way for a new chem. functionalization protocol to enhance the potential of SWNTs for further chem. reactions applicable in various fields.
BibTeX:
@article{Darabi2009,
author = {Darabi, Hossein Reza and Mohandessi, Shabnam and Aghapoor, Kioumars and Mohsenzadeh, Farshid and Karouei, Mohammad Hashemi and Tahoori, Fatemeh and Herges, Rainer},
title = {Thioamidation of Single-Walled Carbon Nanotubes: a New Chemical Functionalization Protocol by the Willgerodt-Kindler Reaction.},
journal = {Aust. J. Chem.},
year = {2009},
volume = {62},
pages = {413-418},
doi = {http://doi.org/10.1071/CH08318}
}
Synthesis, crystal structure and silver complexation of a novel saddle-shaped stilbenophane: NMR and theoretical study on the complex.
H.R. Darabi, M.A. Arani, A. Motamedi, R. Firouzi, R. Herges, A.R. Mohebbi, S.M. Nasseri and C. Nather, Supramol. Chem. 2009, 21, 632-637.
Abstract:
A new Z,Z-stilbenophane was synthesized and characterised. According to an X-ray structure anal., the structure has a saddle shape, with the π-electrons of the double bonds and the oxygen atoms pointing towards the center of a cavity. The ligand forms a 1:1 complex with Ag+. Both NMR spectra and theor. anal. (Gauge-independent AOs (GIAO) and Quantum theory of atoms in mols. (QTAIM)) suggest that the silver cation is bound within the mol. cavity. The metal is coordinated by the two olefinic double bonds and the four oxygen atoms in an approx. octahedral environment. The coordination motif is unusual because the soft silver cation prefers the interaction with the four hard oxygen atoms over the bonding to the arene units, which is frequently obsd. in Ag+ arene complexes.
BibTeX:
@article{Darabi2009a,
author = {Darabi, Hossein Reza and Arani, Marjan Azimzadeh and Motamedi, Abbas and Firouzi, Rohoullah and Herges, Rainer and Mohebbi, Ali Reza and Nasseri, Sarah M. and Nather, Christian.},
title = {Synthesis, crystal structure and silver complexation of a novel saddle-shaped stilbenophane: NMR and theoretical study on the complex.},
journal = {Supramol. Chem.},
year = {2009},
volume = {21},
pages = {632-637},
doi = {http://doi.org/10.1080/10610270802657650}
}
Controlled Formation of an Axially Bonded Co-Phthalocyanine Dimer.
X. Ge, C. Manzano, R. Berndt, L.T. Anger, F. Kohler and R. Herges, J. Am. Chem. Soc. 2009, 131, 6096-6098.
Abstract:
Isolated Co-phthalocyanine (CoPc) mols. were moved on a monolayer of CoPc on Cu(111) using an STM tip. If placed almost on top of another, the CoPc mol. in the 2nd layer locks in place and the STM image at neg. bias changes substantially. D. functional theory calcns. explain the nature of the bonding mode and the change in STM.
BibTeX:
@article{Ge2009,
author = {Ge, Xin and Manzano, Carlos and Berndt, Richard and Anger, Lennart T. and Kohler, Felix and Herges, Rainer},
title = {Controlled Formation of an Axially Bonded Co-Phthalocyanine Dimer.},
journal = {J. Am. Chem. Soc.},
year = {2009},
volume = {131},
pages = {6096-6098},
doi = {http://doi.org/10.1021/ja900484c}
}
2-(2,4-Dinitrobenzyl)pyridine (DNBP): A Potential Light-Activated Proton Shuttle.
C. Goeschen, R. Herges, J. Richter, B. Tokarczyk and J. Wirz, Helv. Chim. Acta 2009, 92, 1909-1922.
Abstract:
The well-known photochromic tautomerism of 2-(2,4-dinitrobenzyl)pyridine (1; CH; Scheme 1) was re-investigated by flash photolysis in aq. soln. in view of its potential application as a light-activated proton pump. Irradn. of 1 yields the enamine tautomer NH (λmax = 520 nm) that rapidly equilibrates with its conjugate base CNO- (λmax = 420 nm). The pH-rate profile for the first-order decay of NH and CNO- provides a direct detn. of the acidity const. of NH, pKa,cNH = 5.94±0.12 (I = 0.1M) and serves to clarify the mechanisms of proton transfer prevailing in aq. solns. The acidity const. of protonated 1 (CHNH+), pKa,cCHNH = 4.18 ± 0.02, was detd. by spectrophotometric titrn.
BibTeX:
@article{Goeschen2009,
author = {Goeschen, Catrin and Herges, Rainer and Richter, Josef and Tokarczyk, Bogdan and Wirz, Jakob},
title = {2-(2,4-Dinitrobenzyl)pyridine (DNBP): A Potential Light-Activated Proton Shuttle.},
journal = {Helv. Chim. Acta},
year = {2009},
volume = {92},
pages = {1909-1922},
doi = {http://doi.org/10.1002/hlca.200900191}
}
Gap-mode SERS studies of azobenzene-containing self-assembled monolayers on Au(111).
U. Jung, M. Mueller, N. Fujimoto, K. Ikeda, K. Uosaki, U. Cornelissen, F. Tuczek, C. Bornholdt, D. Zargarani, R. Herges and O. Magnussen, J. Colloid Interface Sci. 2009, 341, 366-375.
Abstract:
Self-assembled monolayers of azobenzene-contg. thiols on smooth Au(1 1 1) surfaces were studied by gap-mode surface-enhanced Raman spectroscopy (gap-mode SERS). By adsorption of colloidal Au nanoparticles on top of the org. adlayer highly reproducible spectra with strongly enhanced intensities are obtained. The obsd. bands indicate a trans conformation of the azobenzene moieties and are in agreement with structural data for the mol. layer. A characteristic dependency on the terminal and the spacer groups of the mols. is found. Samples prepd. during illumination with UV light show pronounced spectral differences that can be attributed to azobenzene in cis conformation.
BibTeX:
@article{Jung2009,
author = {Jung, Ulrich and Mueller, Mathias and Fujimoto, Norihiro and Ikeda, Katsuyoshi and Uosaki, Kohei and Cornelissen, Ursula and Tuczek, Felix and Bornholdt, Claudia and Zargarani, Dordaneh and Herges, Rainer and Magnussen, Olaf},
title = {Gap-mode SERS studies of azobenzene-containing self-assembled monolayers on Au(111).},
journal = {J. Colloid Interface Sci.},
year = {2009},
volume = {341},
number = { },
pages = {366-375},
doi = {http://doi.org/10.1016/j.jcis.2009.09.040}
}
Synthesis of α-Ketoester- and α-Hydroxyester-Substituted Isoindazoles via the Thermodynamic Coarctate Cyclization of Ester-Terminated Azo-Ene-Yne Systems.
S.P. McClintock, N. Forster, R. Herges and M.M. Haley, J. Org. Chem. 2009, 74, 6631-6636.
Abstract:
The synthesis of isoindazoles bearing α-ketoester and α-hydroxyester groups via the coarctate cyclization of ester-terminated azo-ene-yne precursors is described. Whereas previous studies on isoindazole formation have shown the reaction to proceed through a kinetic coarctate pathway, functionalization of the terminal acetylene with a Me ester sufficiently stabilizes the carbene intermediate to make the coarctate cyclization the thermodn. pathway. D. functional theory (DFT) computations reveal ca. 8-9 Kcal mol-1 lower energy transition states for the coarctate pathway compared to the parent system.
BibTeX:
@article{McClintock2009,
author = {McClintock, Sean P. and Forster, Nathan and Herges, Rainer and Haley, Michael M.},
title = {Synthesis of α-Ketoester- and α-Hydroxyester-Substituted Isoindazoles via the Thermodynamic Coarctate Cyclization of Ester-Terminated Azo-Ene-Yne Systems.},
journal = {J. Org. Chem.},
year = {2009},
volume = {74},
pages = {6631-6636},
doi = {http://doi.org/10.1021/jo9011283}
}
Brownian molecular rotors: Theoretical design principles and predicted realizations.
J.B. Schoenborn, R. Herges and B. Hartke, J. Chem. Phys. 2009, 130, 234906/1-234906/6.
Abstract:
We propose simple design concepts for mol. rotors driven by Brownian motion and external photochem. switching. Unidirectionality and efficiency of the motion is measured by explicit simulations. Two different mol. scaffolds are shown to yield viable mol. rotors when decorated with suitable substituents. (c) 2009 American Institute of Physics.
BibTeX:
@article{Schoenborn2009,
author = {Schoenborn, Jan Boyke and Herges, Rainer and Hartke, Bernd},
title = {Brownian molecular rotors: Theoretical design principles and predicted realizations.},
journal = {J. Chem. Phys.},
year = {2009},
volume = {130},
pages = {234906/1-234906/6},
doi = {http://doi.org/10.1063/1.3148223}
}
Chiral Crystallization: Freezing a Rapid Cope Rearrangement in the Solid State.
J. Siegwarth, J. Bornhoft, C. Nather and R. Herges, Org. Lett. 2009, 11, 3450-3452.
Abstract:
Homotropylidene and its derivs. undergo a fast Cope rearrangement. A homotropylidene system (cyclooctatetraene dimer) is reported that racemizes rapidly by such a valence isomerization in soln. at room temp. In the solid state, however, this rearrangement is frozen, and the single crystals pptg. from the racemic soln. contain only one enantiomer. Since very large crystals can be grown, the racemic soln. in principle can be converted into a single enantiomer by crystn.
BibTeX:
@article{Siegwarth2009,
author = {Siegwarth, Jan and Bornhoft, Jan and Nather, Christian and Herges, Rainer},
title = {Chiral Crystallization: Freezing a Rapid Cope Rearrangement in the Solid State.},
journal = {Org. Lett.},
year = {2009},
volume = {11},
pages = {3450-3452},
doi = {http://doi.org/10.1021/ol901326p}
}
Highly Efficient Reversible Z-E Photoisomerization of a Bridged Azobenzene with Visible Light through Resolved S1(nπ*) Absorption Bands.
R. Siewertsen, H. Neumann, B. Buchheim-Stehn, R. Herges, C. Nather, F. Renth and F. Temps, J. Am. Chem. Soc. 2009, 131, 15594-15595.
Abstract:
The reversible Z-E photoswitching properties of the (Z) and (E) isomers of the severely constrained bridged azobenzene deriv. 5,6-dihydrodibenzo[c,g][1,2]diazocine (1) were investigated quant. by UV/vis absorption spectroscopy in soln. in n-hexane. In contrast to normal azobenzene (AB), 1 has well sepd. S1(nπ*) absorption bands, peaking at λZ = 404 nm and λE = 490 nm. Using light at λ = 385 nm, it was found that 1Z can be switched to 1E with very high efficiency, Γ = 92 ± 3%. Conversely, 1E can be switched back to 1Z using light at λ = 520 nm with ∼100% yield. The measured quantum yields are ΦZ→E = 72 ± 4% and ΦE→Z = 50 ± 10%. The thermal lifetime of the (E) isomer is 4.5 ± 0.1 h at 28.5°. The obsd. photochromic and photoswitching properties of 1 are much more favorable than those for normal AB, making the title compd. a promising candidate for interesting applications as a mol. photoswitch esp. at low temps. The severe constraints by the ethylenic bridge apparently do not hinder but favor the Z-E photoisomerization reactions.
BibTeX:
@article{Siewertsen2009,
author = {Siewertsen, Ron and Neumann, Hendrikje and Buchheim-Stehn, Bengt and Herges, Rainer and Nather, Christian and Renth, Falk and Temps, Friedrich.},
title = {Highly Efficient Reversible Z-E Photoisomerization of a Bridged Azobenzene with Visible Light through Resolved S1(nπ*) Absorption Bands.},
journal = {J. Am. Chem. Soc.},
year = {2009},
volume = {131},
number = { },
pages = {15594-15595},
doi = {http://doi.org/10.1021/ja906547d}
}
Negligible diradical character for the ultralong C-C bond in 1,1,2,2-tetraarylpyracene derivatives at room temperature.
T. Takeda, H. Kawai, R. Herges, E. Mucke, Y. Sawai, K. Murakoshi, K. Fujiwara and T. Suzuki, Tetrahedron Lett. 2009, 50, 3693-3697.
Abstract:
There is evidence that the cryst.-state thermochromic behavior of dispiropyracene acr-1 with an ultralong C-C bond [1.791(3) Å at 413 K, 1.771(3) Å at 93 K] might be due to thermal generation of a bond-dissocd. triplet diradical. The C1-C2 bond lengths (d) in the newly prepd. 1,1,2,2-tetraarylpyracenes 1a-e [1.717(4)-1.761(4) Å at 113/123/153 K] are also much larger than the std. value for C(sp3)-C(sp3) (1.54 Å). The fact that there is no correlation between d and the radical-stabilizing parameter (σ.bul.) provides evidence that there is no contribution from a crystallog. artifact caused by contamination of the diradical in the crystal of 1 at room temp. or below. Further indication for the covalent nature of the ultralong C-C bond in tetraphenylpyracene 1c was attained by Raman spectroscopy, showing the far red-shifted C1-C2 stretching vibration (638 cm-1) and by the theor. prediction of very large vertical singlet-triplet energy gap (58.3 kcal mol-1 at the UB3LYP/6-31G* level). However, at elevated temps. bond dissocn. might occur forming a triplet diradical.
BibTeX:
@article{Takeda2009,
author = {Takeda, Takashi and Kawai, Hidetoshi and Herges, Rainer and Mucke, Eva and Sawai, Yoshitaka and Murakoshi, Kei and Fujiwara, Kenshu and Suzuki, Takanori},
title = {Negligible diradical character for the ultralong C-C bond in 1,1,2,2-tetraarylpyracene derivatives at room temperature.},
journal = {Tetrahedron Lett.},
year = {2009},
volume = {50},
pages = {3693-3697},
doi = {http://doi.org/10.1016/j.tetlet.2009.03.202}
}
Transferring Sondheimer's Annulene Chemistry into Three-Dimensional Space.
C. Werner, H. Hopf, J. Grunenberg, L. Ernst, P.G. Jones, F. Koehler and R. Herges, Eur. J. Org. Chem. 2009, 2621-2626.
Abstract:
On treatment with potassium tert-butoxide in tert-Bu alc. the two [6.6]paracyclophanes 10 and 11 isomerize to 12 and 13, resp., [6.6]paracyclophanes with fully conjugated bridges, thus transferring the Sondheimer annulene chem. to three-dimensional space. The structures of the new hydrocarbons were established by spectroscopic data (12, 13) and X-ray structural anal. (13) as well as by computational methods. According to ACID calcns. these three-dimensional aroms. are not Moebius systems.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009).
BibTeX:
@article{Werner2009,
author = {Werner, Christian and Hopf, Henning and Grunenberg, Joerg and Ernst, Ludger and Jones, Peter G. and Koehler, Felix and Herges, Rainer},
title = {Transferring Sondheimer's Annulene Chemistry into Three-Dimensional Space.},
journal = {Eur. J. Org. Chem.},
year = {2009},
pages = {2621-2626},
doi = {http://doi.org/10.1002/ejoc.200900138}
}
Synthesis of annulenes via multiple Wittig reactions; in-situ dimerization of 1,2;5,6-dibenzocyclooctatetraene.
J. Bornhoeft, J. Siegwarth, C. Nather and R. Herges, Eur. J. Org. Chem. 2008, 1619-1624.
Abstract:
A simple synthetic route to tetrabenzo[16]- and hexabenzo[24]annulene systems using one-pot multiple Wittig reactions is presented. The structure of the all-trans-isomer of tetrabenzo[16]annulene was characterized by NMR spectroscopy and X-ray diffraction. Three isomers of an unexpected dibenzocyclooctatetraene dimer product were also isolated and identified by NMR and X-ray diffraction studies.
BibTeX:
@article{Bornhoeft2008,
author = {Bornhoeft, Jan and Siegwarth, Jan and Nather, Christian and Herges, Rainer.},
title = {Synthesis of annulenes via multiple Wittig reactions; in-situ dimerization of 1,2;5,6-dibenzocyclooctatetraene.},
journal = {Eur. J. Org. Chem.},
year = {2008},
pages = {1619-1624},
doi = {http://doi.org/10.1002/ejoc.200701174}
}
The [12]Annulene Global Minimum.
M.N. Braten, C. Castro, R. Herges, F. Koehler and W.L. Karney, J. Org. Chem. 2008, 73, 1532-1535.
Abstract:
A new global min. for [12]annulene has been computationally located. This mono-trans min. 5 (CCCCCT) is computed to be 1.5 kcal/mol more stable (CCSD(T)/cc-pVDZ//BHHLYP/6-311+G**) than the known tri-trans isomer 1 (CTCTCT) and 2.4 kcal/mol lower than the di-trans isomer 4 (CCTCCT), for which there is indirect evidence. The barriers for several rearrangements of 5 were all computed to be above 15 kcal/mol, indicating that direct exptl. characterization of 5 should be possible. The computed barriers for the dynamic processes (including conformational automerization) coupled with computed 1H NMR shift values should aid in the future characterization of this [12]annulene isomer.
BibTeX:
@article{Braten2008,
author = {Braten, Miles N. and Castro, Claire and Herges, Rainer and Koehler, Felix and Karney, William L.},
title = {The [12]Annulene Global Minimum.},
journal = {J. Org. Chem.},
year = {2008},
volume = {73},
pages = {1532-1535},
doi = {http://doi.org/10.1021/jo702412d}
}
Tetradehydroadamantane-1,3,5,7-Di- and Tetracations and Their Helium and Hydride Inclusion Complexes: Spherical Aromaticity and Evidence for a Bonding Interaction between Carbon and Helium.
G. Bucher, F. Kohler and R. Herges, J. Phys. Chem. A 2008, 112, 9906-9910.
Abstract:
The unusual stability of the exptl. known 1,3-dehydro-5,7-adamantyl dication was previously explained by four-center two-electron aromaticity with three-dimensional (tetrahedral) topol. Magnetic criteria (ACID and ring-current anal.) now demonstrate that there is also a very strong contribution from hyperconjugation with all six methylene bridges. The delocalized system of electrons thus includes all valence electrons, and the structure, therefore, should rather be described as a spherically arom. 50-electron system. The corresponding Td-sym. tetracation with 48 electrons is antiarom. and not a min. structure. With a He atom or a hydride ion at the center of the cage, the tetracation is predicted to form a kinetically stable complex. Magnetic criteria demonstrate that the antiaromaticity is greatly reduced, and a bond anal. hints at bonding interactions between He (and H-) and the carbon atoms of the adamantane cage.
BibTeX:
@article{Bucher2008,
author = {Bucher, Gotz and Kohler, Felix and Herges, Rainer.},
title = {Tetradehydroadamantane-1,3,5,7-Di- and Tetracations and Their Helium and Hydride Inclusion Complexes: Spherical Aromaticity and Evidence for a Bonding Interaction between Carbon and Helium.},
journal = {J. Phys. Chem. A},
year = {2008},
volume = {112},
pages = {9906-9910},
doi = {http://doi.org/10.1021/jp803594w}
}
Homobenzene: Homoaromaticity and Homoantiaromaticity in Cycloheptatrienes.
Z. Chen, H. Jiao, J.I. Wu, R. Herges, S.B. Zhang and P. v.R. Schleyer, J. Phys. Chem. A 2008, 112, 10586-10594.
Abstract:
Cycloheptatriene (Cs) is firmly established to be a neutral homoarom. mol. based on detailed analyses of geometric, energetic, and magnetic criteria. Substituents at the 7 (methylene) position, ranging from the electropos. BH2 to the electroneg. F, favor the equatorial conformation but influence the aromaticity only to a small extent. By the same criteria, the planar transition state (C2v) for cycloheptatriene ring inversion is clearly antiarom. This is attributed to the involvement of the pseudo-2pi-electrons of the CH2 group with the 6pi-electrons of the ring to give an 8pi-electron system. Similarly, the participation of the CH2 groups into C2v cyclopentadiene and cyclononatetraene lead to significant 4n + 2 pi electron aromaticity. The cyclization of cycloheptatriene to norcaradiene proceeds via a highly arom. transition structure, but norcaradiene itself is less arom. than cycloheptatriene. An annelated cyclopropane ring does not function as effectively as a double bond in promoting cyclic electron delocalization.
BibTeX:
@article{Chen2008,
author = {Chen, Zhongfang and Jiao, Haijun and Wu, Judy I. and Herges, Rainer and Zhang, S. B. and Schleyer, Paul von Rague.},
title = {Homobenzene: Homoaromaticity and Homoantiaromaticity in Cycloheptatrienes.},
journal = {J. Phys. Chem. A},
year = {2008},
volume = {112},
pages = {10586-10594},
doi = {http://doi.org/10.1021/jp802496m}
}
Structure and redox behavior of azobenzene-containing monolayers on Au(111): A combined STM, X-ray reflectivity, and voltammetry study.
U. Jung, B. Baisch, D. Kaminski, K. Krug, A. Elsen, T. Weineisen, D. Raffa, J. Stettner, C. Bornholdt, R. Herges and O. Magnussen, J. Electroanal. Chem. 2008, 619-620, 152-158.
Abstract:
A combined structural and electrochem. study of self-assembled monolayers of the azobenzene-contg. alkane thiol N-(2-mercaptoethyl)-4-phenylazobenzamide on Au(111) by scanning tunneling microscopy, synchrotron x-ray reflectivity, and cyclic voltammetry is presented. Densely packed monolayers are obsd., in which the mols. are arranged in chains forming an ordered (13 * 3) structure with a coverage of 2/7 ML. The mols. are tilted by 40 Deg relative to the surface normal, resulting in a monolayer thickness of 13.7 .ANG.. A total charge of 65.2 +- 4.3 micro C/cm2 corresponding to 1e- per mol. and apparent electron transfer coeffs. of  0.5 are found.
BibTeX:
@article{Jung2008,
author = {Jung, Ulrich and Baisch, Belinda and Kaminski, Daniel and Krug, Klaus and Elsen, Annika and Weineisen, Tobias and Raffa, Diego and Stettner, Jochim and Bornholdt, Claudia and Herges, Rainer and Magnussen, Olaf.},
title = {Structure and redox behavior of azobenzene-containing monolayers on Au(111): A combined STM, X-ray reflectivity, and voltammetry study.},
journal = {J. Electroanal. Chem.},
year = {2008},
volume = {619-620},
pages = {152-158},
doi = {http://doi.org/10.1016/j.jelechem.2008.04.002}
}
Computational analysis of the dual reactivity of conjugated hetero-'ene-ene-yne' systems.
S.P. McClintock, L.D. Shirtcliff, R. Herges and M.M. Haley, Abstracts of Papers, 235th ACS National Meeting, New Orleans, LA, United States, April 6-10, 2008 2008, ORGN-409.
Abstract:
There is considerable interest in the synthesis of heterocyclic compds. derived from hetero--ene-ene-yne' precursors. The ring forming reactions often follow unusual reaction mechanisms and afford hard to obtain substitution patterns. Work in our lab with azo-ene-yne compds. has examd. the dual reactivity of these systems to yield either five- or six-membered heterocycles. Recent work has included addn. of nitroso and nitrile moieties into the scaffolds. This paper extends our computational investigations by examg. a new series of hetero--ene-ene-yne' and all-carbon -ene-ene-yne' precursor systems for potential exptl. study.
BibTeX:
@conference{McClintock2008,
author = {McClintock, Sean P. and Shirtcliff, Laura D. and Herges, Rainer and Haley, Michael M.},
title = {Computational analysis of the dual reactivity of conjugated hetero-'ene-ene-yne' systems.},
journal = {Abstracts of Papers, 235th ACS National Meeting, New Orleans, LA, United States, April 6-10, 2008},
year = {2008},
pages = {ORGN-409}
}
Vibrational properties of semitrimer picotubes.
N. Rosenkranz, M. Machon, R. Herges and C. Thomsen, Chem. Phys. Lett. 2008, 451, 249-251.
Abstract:
The semitrimer picotube is a ring-shaped hydrocarbon closely related to a very short (3,3) C nanotube. The authors study the vibrational properties of the semitrimer by Raman spectroscopy and find the structural similarity to nanotubes to be reflected also in the vibrational spectra. In particular, combining polarization-dependent Raman measurements and ab initio calcns. the authors can identify a fully sym. vibration corresponding to the radial breathing mode in nanotubes.
BibTeX:
@article{Rosenkranz2008,
author = {Rosenkranz, N. and Machon, M. and Herges, R. and Thomsen, C.},
title = {Vibrational properties of semitrimer picotubes.},
journal = {Chem. Phys. Lett.},
year = {2008},
volume = {451},
pages = {249-251},
doi = {http://doi.org/10.1016/j.cplett.2007.12.002}
}
Azo Supramolecules on Au(111) with Controlled Size and Shape.
Y. Wang, X. Ge, G. Schull, R. Berndt, C. Bornholdt, F. Koehler and R. Herges, J. Am. Chem. Soc. 2008, 130, 4218-4219.
Abstract:
Using a subtle balance between weak intermol. C-H...N hydrogen bonds and mol.-surface interactions, supramols. of azobenzene-related mols. on Au surfaces were prepd. For anal., modeling based on 1st-principles calcns. was performed.
BibTeX:
@article{Wang2008,
author = {Wang, Yongfeng and Ge, Xin and Schull, Guillaume and Berndt, Richard and Bornholdt, Claudia and Koehler, Felix and Herges, Rainer.},
title = {Azo Supramolecules on Au(111) with Controlled Size and Shape.},
journal = {J. Am. Chem. Soc.},
year = {2008},
volume = {130},
pages = {4218-4219},
doi = {http://doi.org/10.1021/ja710414b%20S0002-7863(71)00414-1}
}
Comment on "Origin of the nonplanarity of tetrafluoro cyclobutadiene, C4F4"
K. Felix, H. Rainer and S. Amnon, J. Phys. Chem. A 2007, 111, 5116-8; discussion 5119-21..
BibTeX:
@article{Felix,
author = {Felix, Koehler and Rainer, Herges and Amnon, Stanger},
title = {Comment on "Origin of the nonplanarity of tetrafluoro cyclobutadiene, C4F4"},
journal = {J. Phys. Chem. A},
year = {2007},
volume = {111},
pages = {5116-8; discussion 5119-21.},
doi = {http://doi.org/10.1021/jp070372v}
}
Identification of flavonoids and hydroxycinnamic acids in pak choi varieties (Brassica campestris L. ssp. chinensis var. communis) by HPLC-ESI-MSn and NMR and their quantification by HPLC-DAD.
B. Harbaum, E.M. Hubbermann, C. Wolff, R. Herges, Z. Zhu and K. Schwarz, J. Agric. Food Chem. 2007, 55, 8251-8260.
Abstract:
Twenty-eight polyphenols, 11 flavonoid derivs. and 17 hydroxycinnamic acid derivs., were detected in different cultivars of the Chinese cabbage pak choi, Brassica campestris L. ssp. chinensis var. communis, by HPLC-DAD-ESI-MSh. Kaempferol was the major flavonoid in pak choi, glycosylated and acylated with different compds. Smaller amts. of isorhamnetin were also detected. A structural detn. was carried out by 1H and 13C NMR spectroscopy for the main compd., kaempferol-3-O-hydroxyferuloylsophoroside-7-O-glucoside, for the first time. Hydroxycinnamic acid derivs. were identified as different esters of quinic acid, glycosides, and malic acid. The latter ones are described for the first time in cabbages. The content of polyphenols was detd. in 11 cultivars of pak choi, with higher concns. present in the leaf blade than in the leaf stem. Hydroxycinnamic acid esters, particularly malic acid derivs., are present in both the leaf blade and leaf stem, whereas flavonoid levels were detd. only in the leaf blade.
BibTeX:
@article{Harbaum2007,
author = {Harbaum, Britta and Hubbermann, Eva Maria and Wolff, Christian and Herges, Rainer and Zhu, Zhujun and Schwarz, Karin.},
title = {Identification of flavonoids and hydroxycinnamic acids in pak choi varieties (Brassica campestris L. ssp. chinensis var. communis) by HPLC-ESI-MSn and NMR and their quantification by HPLC-DAD.},
journal = {J. Agric. Food Chem.},
year = {2007},
volume = {55},
pages = {8251-8260},
doi = {http://doi.org/10.1021/jf071314+}
}
Rational synthesis of carbon nanotubes.
R. Herges, Nachr. Chem. 2007, 55, 962-963,966-969.
Abstract:
A review. Strategies for the prepn. of different kinds of C nanotubes are summarized. It is distinguished between open and closed nanotubes, armchairs, and zigzag structures. Belt- or tubular compds. can be prepd. by stacking of rings or connecting concave components. The prepn. of a subunit for (4,4)-armchair nanotubes or picotubes is described. Problems with the cyclodehydrogenation step are addressed. Furthermore, the prepn. of fullerene hemispheres called buckybowls is treated. The buckybowls could be used as templates for CVD processes. The application of nanotubes as transistors is briefly mentioned. Finally, a strategy of Smalley et al. (2006) is illustrated for the propagation of nanotubes and the prepn. of single peculiar types of them.
BibTeX:
@article{Herges2007a,
author = {Herges, Rainer.},
title = {Rational synthesis of carbon nanotubes.},
journal = {Nachr. Chem.},
year = {2007},
volume = {55},
pages = {962-963,966-969}
}
Origin of the Nonplanarity of Tetrafluoro Cyclobutadiene, C4F4. Comment.
F. Koehler, R. Herges and A. Stanger, J. Phys. Chem. A 2007, 111, 5116-5118.
Abstract:
A polemic. Energetic considerations, NICS-scans, and ACID ( anisotropy of induced c.d.) analyses prove that the title compd. is not arom., as is claimed by Seal and Chakrabarti (2007).
BibTeX:
@article{Koehler2007,
author = {Koehler, Felix and Herges, Rainer and Stanger, Amnon.},
title = {Origin of the Nonplanarity of Tetrafluoro Cyclobutadiene, C4F4. Comment.},
journal = {J. Phys. Chem. A},
year = {2007},
volume = {111},
pages = {5116-5118},
doi = {http://doi.org/10.1021/jp070372v%20S1089-5639(07)00372-6}
}
Organic chemistry: aromatics with a twist
H. Rainer, Nature 2007, 450, 36-7..
BibTeX:
@article{Rainer,
author = {Rainer, Herges},
title = {Organic chemistry: aromatics with a twist},
journal = {Nature},
year = {2007},
volume = {450},
pages = {36-7.},
doi = {http://doi.org/10.1038/450036a}
}
CuCl-Induced Formation and Migration of Isoindazolyl Carbenoids.
L.D. Shirtcliff, M.M. Haley and R. Herges, J. Org. Chem. 2007, 72, 2411-2418.
Abstract:
Two azo-ene-butadiyne conjugated systems, e.g., 1-(Et2NN:N)-4-Cl-C6H4-2-C==CC==CR (R = Ph, 2-biphenyl), undergo CuCl-mediated cyclization to afford isoindazolyl carbenoids that could be trapped with 2,3-dimethyl-2-butene as [2 + 1] cycloaddn. products, e.g., I. X-ray structure anal. of the resultant cyclopropanes I showed that formal migration to the distal carbenoid isomer and subsequent trapping had occurred. The possible CuCl-induced cyclization/migration pathways were explored using d. functional theory, which indicated that the reaction most likely occurred via coordination of CuCl to the distal alkyne bond.
BibTeX:
@article{Shirtcliff2007,
author = {Shirtcliff, Laura D. and Haley, Michael M. and Herges, Rainer.},
title = {CuCl-Induced Formation and Migration of Isoindazolyl Carbenoids.},
journal = {J. Org. Chem.},
year = {2007},
volume = {72},
pages = {2411-2418},
doi = {http://doi.org/10.1021/jo0622274}
}
DFT study of cycloaddition reaction of isothiocyanates with diazoazoles to 4-imino-4H-pyrazolo[5,1-d] [1,2,3,5]thiatriazines.
J.O. Subbotina, E.V. Sadchikova, V.A. Bakulev, W.M.F. Fabian and R. Herges, Int. J. Quantum Chem. 2007, 107, 2479-2488.
Abstract:
The mechanism of reaction of isothiocyanates with diazopyrazoles to 4-imino-4H-pyrazolo[5,1-d] [1,2,3,5]thiatriazines was investigated. It was suggested that the reaction proceeds via a pseudopericyclic cycloaddn. with activation barrier of .apprx.31 kcal mol-1 (B3LYP/6-31G*). The mechanism was confirmed by NBO and ACID schemes. The question of regioselectivity was also explored. It was shown that an acyl substituent on the isothiocyanate led to a stabilization of the final product due to S...O interaction.
BibTeX:
@article{Subbotina2007,
author = {Subbotina, Julia O. and Sadchikova, Elena V. and Bakulev, Vasiliy A. and Fabian, Walter M. F. and Herges, Rainer.},
title = {DFT study of cycloaddition reaction of isothiocyanates with diazoazoles to 4-imino-4H-pyrazolo[5,1-d] [1,2,3,5]thiatriazines.},
journal = {Int. J. Quantum Chem.},
year = {2007},
volume = {107},
pages = {2479-2488},
doi = {http://doi.org/10.1002/qua.21351}
}
The existence of secondary orbital interactions.
C.S. Wannere, A. Paul, R. Herges, K.N. Houk, I. Schaefer, Henry F. and P. v.R. Schleyer, J. Comput. Chem. 2007, 28, 344-361.
Abstract:
B3LYP/6-311+G** (and MP2/6-311+G**) computations, performed for a series of Diels-Alder (DA) reactions, confirm that the endo transition states (TS) and the related Cope-TSs are favored energetically over the resp. exo-TSs. Likewise, the computed magnetic properties (nucleus-independent chem. shifts and magnetic susceptibilities) of the endo- (as well as the Cope) TS's reveal their greater electron delocalization and greater aromaticity than the exo-TS's. However, Woodward and Hoffmann's original example is an exception: their endo-TS model, involving the DA reaction of a syn- with an anti-butadiene (BD), actually is disfavored energetically over the corresponding exo-TS; magnetic criteria also do not indicate the existence of SOI delocalization in either case. Instead, a strong energetic preference for endo-TSs due to SOI is found when both BDs are in the syn conformations. This is in accord with Alder and Stein's rule of "max. accumulation of double bonds:" both the dienophile and the diene should have syn conformations. Plots along the IRC's show that the magnetic properties typically are most strongly exalted close to the energetic TS. Because of SOI, all the points along the endo reaction coordinates are more diatropic than along the corresponding exo pathways. We find weak SOI effects to be operative in the endo-TSs involved in the cycloaddns. of cyclic alkenes, cyclopropene, aziridine, cyclobutene, and cyclopentene, with cyclopentadiene. While the endo-TSs are only slightly lower in energy than the resp. exo-TSs, the magnetic properties of the endo-TS's are significantly exalted over those for the exo-TS's and the Natural Bond Orbitals indicate small stabilizing interactions between the methylene cycloalkene hydrogen orbitals (and lone pairs in case of aziridine) with pi-character and the diene pi MOs.
BibTeX:
@article{Wannere2007,
author = {Wannere, Chaitanya S. and Paul, Ankan and Herges, Rainer and Houk, K. N. and Schaefer, Henry F., III and Schleyer, Paul von Rague.},
title = {The existence of secondary orbital interactions.},
journal = {J. Comput. Chem.},
year = {2007},
volume = {28},
pages = {344-361},
doi = {http://doi.org/10.1002/jcc.20532}
}
Synthesis and properties of the first Mobius annulenes.
D. Ajami, K. Hess, F. Koehler, C. Naether, O. Oeckler, A. Simon, C. Yamamoto, Y. Okamoto and R. Herges, Chem.--Eur. J. 2006, 12, 5434-5445.
Abstract:
Heibronner in 1964 predicted that annulenes with "... a planar perimeter of N = 4r AO's, which would yield an open shell configuration when occupied by 4r electrons, can be twisted into a closed shell Mobius strip perimeter without loss in pi electron energy". We have been able to synthesize the first [4n]annulene with such a Mobius topol. and now present further Mobius isomers and the details of their prepn. as stable compds. To address the question whether the twist in the pi system has an effect on the properties we systematically investigate energy, geometry and magnetic parameters of a large no. isomers of [16]annulenes. The Mobius twisted annulenes are consistently more arom. than the non-twisted isomers. This is true for the parent as well as our benzoannulated systems. Our results are in contrast to those published recently.
BibTeX:
@article{Ajami2006,
author = {Ajami, Dariush and Hess, Kirsten and Koehler, Felex and Naether, Christian and Oeckler, Oliver and Simon, Arndt and Yamamoto, Chiyo and Okamoto, Yoshio and Herges, Rainer.},
title = {Synthesis and properties of the first Mobius annulenes.},
journal = {Chem.--Eur. J.},
year = {2006},
volume = {12},
pages = {5434-5445},
doi = {http://doi.org/10.1002/chem.200600215}
}
Experimental and theoretical characterization of the valence isomerization of Bi-2H-azirin-2-yls to diazabenzenes.
K. Banert, S. Grimme, R. Herges, K. Hess, F. Koehler, C.M. Lichtenfeld and E.-U. Wuerthwein, Chem.--Eur. J. 2006, 12, 7467-7481.
Abstract:
3,4-Diazidocyclobutenes were prepd. from the corresponding dihalides. Some of these diazides, such as parent compd. and phenyl-substituted derivs. underwent spontaneous stereoselective electrocyclic ring opening below room temp., whereas the tetraalkyl derivs. had to be heated to force the same reaction. In most cases, the resulting 1,4-diazidobuta-1,3-dienes were isolated to study their photochem. transformation into bi-2H-azirin-2-yls via intermediate monoazirines. Except for starting materials with a low no. of substituents, bi-2H-azirin-2-yls underwent a thermal valence isomerization which led exclusively to pyridazines at surprisingly low temps. Based on quantum-chem. calcns. for the parent bi-2H-azirinyl-2-yl at the UB3LYP/6-31+G(d) and MR-MP2/TZV(2df,2p) levels, the valence isomerization process is best explained by simultaneous homolytic cleavage of both C-N single bonds to generate energetically favorable N,N' diradicals which cyclize to pyridazines. The theor. studies indicate also that one stereoisomer of bi-2H-azirin-2-yl, namely, the rac compd., should undergo valence isomerization more easily than the other, which is in conformity with different rates of these rearrangement reactions found exptl. For the tetramethyl-bi-2H-azirin-2-yls, which are better models for the exptl. studied compds., simultaneous homolytic cleavage of both C-N single bonds is also predicted by the calcns., although the intermediate diradicals are significantly higher in energy than those of the parent system. Safety: care must be taken in handling azides, and a 1,4-diazidobuta-1,3-diene led to a heavy explosion on friction.
BibTeX:
@article{Banert2006,
author = {Banert, Klaus and Grimme, Stefan and Herges, Rainer and Hess, Kirsten and Koehler, Frank and Lichtenfeld, Christian Mueck and Wuerthwein, Ernst-Ulrich.},
title = {Experimental and theoretical characterization of the valence isomerization of Bi-2H-azirin-2-yls to diazabenzenes.},
journal = {Chem.--Eur. J.},
year = {2006},
volume = {12},
pages = {7467-7481},
doi = {http://doi.org/10.1002/chem.200600318}
}
Topology in chemistry: Designing Mobius molecules.
R. Herges, Chem. Rev. (Washington, DC, U. S.) 2006, 106, 4820-4843.
Abstract:
A review discusses non-conjugated mol. Mobius strips, Mobius pi systems (annulenes, cyclacenes, kekulene, transition states), synthesis of the first Mobius annulene, and double twisted pi systems.
BibTeX:
@article{Herges2006,
author = {Herges, Rainer.},
title = {Topology in chemistry: Designing Mobius molecules.},
journal = {Chem. Rev. (Washington, DC, U. S.)},
year = {2006},
volume = {106},
pages = {4820-4843},
doi = {http://doi.org/10.1021/cr0505425}
}
Phane properties of [2.2]paracyclophane/dehydrobenzoannulene hybrids.
H. Hinrichs, A.J. Boydston, P.G. Jones, K. Hess, R. Herges, M.M. Haley and H. Hopf, Chem.--Eur. J. 2006, 12, 7103-7115.
Abstract:
Macrocyclic hybrids of [2.2]paracyclophanes with dehydrobenzo[14]annulenes and dehydro[14]annulenes such as I and II are prepd. The UV/visible absorption spectra of the hybrids are compared to det. the communication between the arom. rings of the paracyclophane units. For some of the title compds. and unsubstituted derivs., the anisotropy of induced c.d. is detd. by calcn. to det. the effect of twisting in the perimeter of the macrocycles on the aromaticity of the component structures. The structures of a tetraethynyl[2.2]paracyclophane and of a twisted macrocyclic annulene are detd. by X-ray crystallog.
BibTeX:
@article{Hinrichs2006,
author = {Hinrichs, Heino and Boydston, Andrew J. and Jones, Peter G. and Hess, Kirsten and Herges, Rainer and Haley, Michael M. and Hopf, Henning.},
title = {Phane properties of [2.2]paracyclophane/dehydrobenzoannulene hybrids.},
journal = {Chem.--Eur. J.},
year = {2006},
volume = {12},
pages = {7103-7115},
doi = {http://doi.org/10.1002/chem.200600498}
}
The transformation of open picotubes to a closed molecular configuration.
C. Schaman, R. Pfeiffer, V. Zolyomi, H. Kuzmany, D. Ajami, R. Herges, O. Dubay and J. Sloan, Phys. Status Solidi B 2006, 243, 3151-3154.
Abstract:
Starting with the open picotube, we studied the interaction of the picotube with carbon nanotubes. The picotube is easily produced at low cost, and therefore an ideal candidate for filling CNTs. The obsd. spectra are in good agreement with the spectra predicted by Gaussian'03 for the closed picotube. The stability of the mol. in two different environments, the inside and the outside of the nanotubes, were investigated in local d. approxn. and inter-mol. Hueckel calcns. We conclude that the closed picotube was formed, and is located on the outside of bundles of nanotubes.
BibTeX:
@article{Schaman2006,
author = {Schaman, Christoph and Pfeiffer, Rudolf and Zolyomi, Viktor and Kuzmany, Hans and Ajami, Daniel and Herges, Rainer and Dubay, Orest and Sloan, Jeremy.},
title = {The transformation of open picotubes to a closed molecular configuration.},
journal = {Phys. Status Solidi B},
year = {2006},
volume = {243},
pages = {3151-3154},
doi = {http://doi.org/10.1002/pssb.200669147}
}
Biscyclization Reactions in Butadiyne- and Ethyne-Linked Triazenes and Diazenes: Concerted versus Stepwise Coarctate Cyclizations.
L.D. Shirtcliff, A.G. Hayes, M.M. Haley, F. Koehler, K. Hess and R. Herges, J. Am. Chem. Soc. 2006, 128, 9711-9721.
Abstract:
A series of alkyne-linked bis-2H-indazoles has been prepd. by the double cyclization of ethyne- or butadiyne-linked phenyltriazene or phenyldiazene moieties. Even though there are two five-membered ring cyclizations and several triple bond shifts involved, the reactions proceed rapidly under neutral conditions with mild heating, affording the heterocycles in excellent yields. DFT calcns., in agreement with exptl. observations, indicate that the reactions: (1) occur via a very short-lived carbene intermediate, (2) are concerted via an asym. transition state, or (3) are even synchronous, with as many as 16 bonds that are made or broken simultaneously. The biscyclizations presented herein strikingly illustrate the concept of coarctate reactions, the stabilization of transition states by coarctate Moebius aromaticity, the ethynologation principle, and the stereochem. rules.
BibTeX:
@article{Shirtcliff2006,
author = {Shirtcliff, Laura D. and Hayes, Austin G. and Haley, Michael M. and Koehler, Felix and Hess, Kirsten and Herges, Rainer.},
title = {Biscyclization Reactions in Butadiyne- and Ethyne-Linked Triazenes and Diazenes: Concerted versus Stepwise Coarctate Cyclizations.},
journal = {J. Am. Chem. Soc.},
year = {2006},
volume = {128},
pages = {9711-9721},
doi = {http://doi.org/10.1021/ja054547v}
}
1,7-cyclization of 1-diazo-2,4-pentadiene and its heteroanalogues: DFT study.
J.O. Subbotina, V.A. Bakulev, R. Herges and W.M.F. Fabian, Int. J. Quantum Chem. 2006, 106, 2229-2235.
Abstract:
1,7-Dipolar cyclizations of 1-diazo-2,4-pentadiene 1a and its heteroanalogues 1b,c and 4c were studied using d. functional theory (DFT). Although the heteroanalogue 1c has an appropriate electronic structure to allow for pseudopericyclic cyclization, natural bond order (NBO) anal. has provided evidence for the electrocyclic ring closure. Magnetic criteria (anisotropy of the induced c.d. [ACID], nucleus-independent chem. shifts [NICS]) confirmed the pericyclic character of the located transition states 2a,c and 5c. The activation barriers for the cyclization of 1-diazo-2,4-pentadiene 1a and its aza analogs 1c, 4c are 3.3, 8.2, and 12.3 kcal/mol at the B3LYP/6-31G(d) level, resp. The higher barrier of the 1c->3c and 4c->3c reactions compared with 1a->3a is in line with the Hammond postulate. The out-of-plane distorted geometry of the cyclic product is an addnl. factor arguing against a pseudopericyclic mechanism.
BibTeX:
@article{Subbotina2006,
author = {Subbotina, Julia O. and Bakulev, V. A. and Herges, R. and Fabian, W. M. F.},
title = {1,7-cyclization of 1-diazo-2,4-pentadiene and its heteroanalogues: DFT study.},
journal = {Int. J. Quantum Chem.},
year = {2006},
volume = {106},
pages = {2229-2235}
}
Organic chemistry in the ChemgaPedia encyclopaedia: Useful visualization tools for e-teaching and e-learning.
T. Winkler and R. Herges, Abstracts of Papers, 232nd ACS National Meeting, San Francisco, CA, United States, Sept. 10-14, 2006 2006, CINF-107.
Abstract:
The ChemgaPedia encyclopaedia is based on the project -Vernetztes Studium - Chemie" (VS-C, -networked chem. studies"). Starting in 1999, 16 workgroups from Germany, Switzerland and Great Britain created substantial learning material covering all aspects of chem. and related topics. Currently, there are 15000 pages and 25000 media files available (graphics, movie clips, 3D models, animations, www.chemgapedia.de). After the official termination of the VS-C project at the end of 2004, the project coordinator FIZ CHEMIE Berlin is continuing the development towards the ChemgaPedia learning system. Org. chem. was represented by the workgroups of Prof. Gregor Fels (Paderborn, Germany) and Prof. Rainer Herges (Kiel, Germany), who closely collaborated, sharing their resp. results and expertise. The aim of our material is to enhance the visualization of org. reactions and structures and thus to improve their comprehensibility. Furthermore, streaming video clips, optional exercises, a search function and a glossary section add to the value of this learning system.
BibTeX:
@conference{Winkler2006,
author = {Winkler, Torsten and Herges, Rainer.},
title = {Organic chemistry in the ChemgaPedia encyclopaedia: Useful visualization tools for e-teaching and e-learning.},
journal = {Abstracts of Papers, 232nd ACS National Meeting, San Francisco, CA, United States, Sept. 10-14, 2006},
year = {2006},
pages = {CINF-107}
}
Organic chemistry 2004.
R. Brueckner, F. Wuerthner, C. Tschierske, A. Krueger, R. Herges, K. Ditrich, R. Pfau, H. Priepke, U. Beifuss, S. Braese, A. Marx, A. Kirschning, N. Sewald, M.O. Senge, T.J.J. Mueller, T. Bach, H. Heydt, J. Hartung, P.R. Schreiner, R. Gschwind, D.A. Plattner, M. Broenstrup, B. Goldfuss, A. Gansaeuer, M. Oestreich, J. Pietruszka, T. Lindel, M. Mueller, E. Weinhold, F. Hausch, A. Jaeschke and M. Albrecht, Nachr. Chem. 2005, 53, 251-272.
Abstract:
A review. In 26 contributions, the progress in org. chem. in the year 2004 is summarized. The following sections in org. chem. are surveyed: org. solids, materials, and liq. crystals; nanostructures and nano-architecture; bulk products, fine chems., and commodities; pharmaceuticals; org. dyes; solid phase synthesis; nucleosides, nucleotides, and oligonucleotides; oligosaccharides; peptides and peptidomimetics; porphyrins and other pyrrole dyes; heterocycles; photochem.; radical chem.; computational org. chem.; NMR spectroscopy; MS spectrometry; reaction mechanisms (without metalorg. chem.); metalorg. chem. (structures and mechanisms, metal-assisted syntheses); metal-free syntheses; natural products (total syntheses, structure elucidation); enzymes in org. synthesis; enzyme mechanisms and models/novel proteins and their functions; bio-combinatorial chem.; and supramol. chem./mol. recognition.
BibTeX:
@article{Brueckner2005,
author = {Brueckner, Reinhard and Wuerthner, Frank and Tschierske, Carsten and Krueger, Anke and Herges, Rainer and Ditrich, Klaus and Pfau, Roland and Priepke, Henning and Beifuss, Uwe and Braese, Stefan and Marx, Andreas and Kirschning, Andreas and Sewald, Norbert and Senge, Mathias O. and Mueller, Thomas J. J. and Bach, Thorsten and Heydt, Heinrich and Hartung, Jens and Schreiner, Peter R. and Gschwind, Ruth and Plattner, Dietmar A. and Broenstrup, Mark and Goldfuss, Bernd and Gansaeuer, Andreas and Oestreich, Martin and Pietruszka, Joerg and Lindel, Thomas and Mueller, Michael and Weinhold, Elmar and Hausch, Felix and Jaeschke, Andres and Albrecht, Markus.},
title = {Organic chemistry 2004.},
journal = {Nachr. Chem.},
year = {2005},
volume = {53},
pages = {251-272}
}
Anisotropy of the Induced Current Density (ACID), a General Method To Quantify and Visualize Electronic Delocalization.
D. Geuenich, K. Hess, F. Koehler and R. Herges, Chem. Rev. (Washington, DC, U. S.) 2005, 105, 3758-3772.
Abstract:
A review. The ACID method is an intuitive and generally applicable method for the investigation and visualization of electron delocalization and bond conjugation in ground, excited and transition states. In the prototype examples for different types of delocalization presented in this review, the ACID anal. is in agreement with previous alternative theor. studies.
BibTeX:
@article{Geuenich2005,
author = {Geuenich, Daniel and Hess, Kirsten and Koehler, Felix and Herges, Rainer.},
title = {Anisotropy of the Induced Current Density (ACID), a General Method To Quantify and Visualize Electronic Delocalization.},
journal = {Chem. Rev. (Washington, DC, U. S.)},
year = {2005},
volume = {105},
pages = {3758-3772},
doi = {http://doi.org/10.1021/cr0300901}
}
cis-Bromination of alkynes without cationic intermediates.
R. Herges, A. Papafilippopoulos, K. Hess, C. Chiappe, D. Lenoir and H. Detert, Angew. Chem., Int. Ed. 2005, 44, 1412-1416, S1412/1-S1412/10.
Abstract:
Surprising insight into a classical mechanism is provided by theor. and exptl. investigations on the bromination of alkynes. In nonpolar solvents the bromination of acetylene via a covalent tribromide adduct is strongly favored over the textbook mechanism via a bridged bromirenium ion. The structurally interesting intermediate explains the syn selectivity of the bromination of strained cycloalkynes.
BibTeX:
@article{Herges2005,
author = {Herges, Rainer and Papafilippopoulos, Andrea and Hess, Kirsten and Chiappe, Cinzia and Lenoir, Dieter and Detert, Heiner.},
title = {cis-Bromination of alkynes without cationic intermediates.},
journal = {Angew. Chem., Int. Ed.},
year = {2005},
volume = {44},
pages = {1412-1416, S1412/1-S1412/10},
doi = {http://doi.org/10.1002/anie.200461632}
}
Moebius, Escher, Bach - the endless tape in art and science.
R. Herges, Naturwiss. Rundsch. 2005, 58, 301-310.
Abstract:
A review is given on the Mobius band and attempts to create mols. with Mobius topol. The occurrence of the twisted, infinite band in mathematics, technique, and art is described. Theor. basics are discussed responsible for difficulties to synthesize org. mols. with Mobius topol. The metathesis strategy of the synthesis of arom. mols. with Mobius topol. is characterized.
BibTeX:
@article{Herges2005a,
author = {Herges, Rainer.},
title = {Moebius, Escher, Bach - the endless tape in art and science.},
journal = {Naturwiss. Rundsch.},
year = {2005},
volume = {58},
pages = {301-310}
}
Phonons and symmetry properties of (4,4) picotube crystals.
M. Machon, S. Reich, J. Maultzsch, R. Herges and C. Thomsen, AIP Conf. Proc. 2005, 786, 452-455.
Abstract:
The recently grown picotube crystals are the closest to a monochiral nanotube sample achieved up to now. We present an exptl. and theor. study of the vibrational properties of these crystals, including polarization dependent Raman spectra and ab initio calcns. We assign symmetries to the most intense peaks, A1 in most cases. From ab initio calcns. we obtain the underlying at. displacements. We find, among others, modes related to the high-energy mode and the radial-breathing mode of carbon nanotubes.
BibTeX:
@conference{Machon2005,
author = {Machon, M. and Reich, S. and Maultzsch, J. and Herges, R. and Thomsen, C.},
title = {Phonons and symmetry properties of (4,4) picotube crystals.},
journal = {AIP Conf. Proc.},
year = {2005},
volume = {786},
pages = {452-455}
}
Structural, electronic, and vibrational properties of (4,4) picotube crystals.
M. Machon, S. Reich, J. Maultzsch, H. Okudera, A. Simon, R. Herges and C. Thomsen, Phys. Rev. B: Condens. Matter Mater. Phys. 2005, 72, 155402/1-155402/11.
Abstract:
The picotube mol. is a highly sym. hydrocarbon, closely related to a very short (4,4) carbon nanotube. We present a thorough exptl. and theor. study of the phys. properties of picotube crystals. In x-ray diffraction expts. we find the picotube mols. to display D2d symmetry. We identify the most intense Raman peaks as A1 modes with polarization-dependent Raman measurements. Ab initio calcns. of the structural, electronic, and vibrational properties of picotubes are in excellent agreement with our expts. We assign the measured vibrations to displacement eigenvectors including those analogous to the nanotube high-energy mode, the D mode, and the radial-breathing mode.
BibTeX:
@article{Machon2005a,
author = {Machon, M. and Reich, S. and Maultzsch, J. and Okudera, H. and Simon, A. and Herges, R. and Thomsen, C.},
title = {Structural, electronic, and vibrational properties of (4,4) picotube crystals.},
journal = {Phys. Rev. B: Condens. Matter Mater. Phys.},
year = {2005},
volume = {72},
pages = {155402/1-155402/11},
doi = {http://doi.org/10.1103/PhysRevB.72.155402}
}
Femtosecond fluorescence up-conversion spectroscopy of a rotation-restricted azobenzene after excitation to the S1 state.
T. Pancur, F. Renth, F. Temps, B. Harbaum, A. Krueger, R. Herges and C. Naether, Phys. Chem. Chem. Phys. 2005, 7, 1985-1989.
Abstract:
Femtosecond time-resolved fluorescence up-conversion spectroscopy has been used in a study of the photo-induced isomerization reactions of a rotation-restricted trans-azobenzene (trans-AB) deriv. capped by a crown ether (I), a chem. similar open deriv. (II), and unsubstituted trans-AB (3) after excitation to the S1 (npi*) state at l = 475 nm in dioxane soln. The obsd. biexponential temporal fluorescence profiles for I and II were almost indistinguishable within exptl. error. The fitted fast fluorescence decay times (+-2s) for the two compds. were t1 (I) = (0.79 +- 0.20) and t1 (II) = (1.05 +- 0.20) ps, compared to t1 (3) = (0.37 +- 0.06) ps. The second decay components could be described with t2 (I) = (20.3 +- 9.5) resp. t2 (II) = (19.0 +- 6.0) ps, vs. t2 (3) = (3.26 +- 0.85) ps. The very similar lifetimes strongly suggest that trans-cis isomerization of I and II after S1 excitation is governed by the same mechanism. Since I cannot isomerize by a simple large-amplitude rotation of one of the Ph rings about the central NN bond, the isomerization dynamics of both ABs should be better described as "inversion" at the N atom(s) rather than large-amplitude "rotation".
BibTeX:
@article{Pancur2005,
author = {Pancur, T. and Renth, F. and Temps, F. and Harbaum, B. and Krueger, A. and Herges, R. and Naether, Chr.},
title = {Femtosecond fluorescence up-conversion spectroscopy of a rotation-restricted azobenzene after excitation to the S1 state.},
journal = {Phys. Chem. Chem. Phys.},
year = {2005},
volume = {7},
pages = {1985-1989},
doi = {http://doi.org/10.1039/b419236b}
}
Raman scattering and electronic properties of the cyclic anthracene tetramer (picotube).
C. Schaman, F. Simon, H. Kuzmany, D. Ajami, K. Hess, R. Herges, O. Dubay and G. Kresse, AIP Conf. Proc. 2005, 786, 186-189.
Abstract:
We present a study on the electronic and vibrational properties of the cyclic anthracene tetramer. FTRaman and Raman spectroscopy in the visible were used to investigate the vibrational properties of the mol. Gaussian'98 and Gaussian'03 were employed to calc. the Raman response; the electronic properties were modeled by VASP, resulting in a gap energy of Eg = 2.24 eV. A strong correlation of the calcd. modes to the measured Raman frequencies provides evidence for the D2d symmetry.
BibTeX:
@conference{Schaman2005,
author = {Schaman, Ch. and Simon, F. and Kuzmany, H. and Ajami, D. and Hess, K. and Herges, R. and Dubay, O. and Kresse, G.},
title = {Raman scattering and electronic properties of the cyclic anthracene tetramer (picotube).},
journal = {AIP Conf. Proc.},
year = {2005},
volume = {786},
pages = {186-189}
}
"Chickenwire" approach for the design of anion receptors.
R. Herges, A. Dikmans, U. Jana, T. Fricke and B. Konig, Abstracts of Papers, 227th ACS National Meeting, Anaheim, CA, United States, March 28-April 1, 2004 2004, IEC-046.
Abstract:
We present a novel approach for the rational design of anion receptors. Our strategy was tested by the synthesis of a nitrate binding ligand. Nitrate has 6 H bond acceptor positions. The optimum spatial arrangement of the complementary H bond donors was detd. by placing "test H bond donors" (HCl) around the nitrate mol. and by optimization of the complex geometry using DFT calcns. Our "chickenwire approach", is based on a coarse cut from a graphite lattice and a subsequent "fine tuning" by variation of the spacer groups X to match the calcd. optimum geometry. The as designed macrocycle (X=O) was synthesized and tested. To our knowledge it is the first neutral nitrate ligand that is able to ext. nitrate from water and that transports NO3- as a carrier through lipophilic membranes. The ligand was successfully applied as an anionic ionophore in an ion sensitive electrode.
BibTeX:
@conference{Herges2004,
author = {Herges, Rainer and Dikmans, A. and Jana, U. and Fricke, T. and Konig, B.},
title = {"Chickenwire" approach for the design of anion receptors.},
journal = {Abstracts of Papers, 227th ACS National Meeting, Anaheim, CA, United States, March 28-April 1, 2004},
year = {2004},
pages = {IEC-046}
}
Approaching the rational synthesis of carbon nanotubes.
R. Herges, D. Ajami and S. Kammermeier, AIP Conf. Proc. 2004, 723, 19-26.
Abstract:
The high temp. methods developed so far, yield heterogeneous mixts. of carbon nanotubes with different length, diam., helicity and with defects alongside with amorphous carbon. Most applications, however, require samples with well defined phys. properties and thus with uniform geometry. Template assisted growth methods and sophisticated purifn. methods not withstanding, many researchers in the field propose that a rational, wet-chem. synthesis should be developed to prep. bulk amts. of uniform nanotubes. We are aiming at this goal for more than 10 years and now present the status of our work. So far our tubes are short (8 A long) substructures of [4,4]armchair tubes which we therefore coined picotubes.
BibTeX:
@article{Herges2004a,
author = {Herges, R. and Ajami, D. and Kammermeier, S.},
title = {Approaching the rational synthesis of carbon nanotubes.},
journal = {AIP Conf. Proc.},
year = {2004},
volume = {723},
pages = {19-26}
}
Fully conjugated beltenes (belt-like and tubular aromatics).
R. Herges, Mod. Cyclophane Chem. 2004, 337-358.
Abstract:
A review. Belt-like and tubular arom. systems can be viewed as an extreme kind of cyclophanes, where both ends are extended and bent in such a way that the two ends meet each other. The syntheses of various fully conjugated beltenes, namely [0n]paracyclophanes 7, mobius belts, and conjugated belts from fullerenes are described.
BibTeX:
@other{Herges2004b,
author = {Herges, R..},
title = {Fully conjugated beltenes (belt-like and tubular aromatics).},
journal = {Mod. Cyclophane Chem.},
year = {2004},
pages = {337-358}
}
Nanostructures and nanoarchitecture.
A. Krueger and R. Herges, Nachr. Chem. 2004, 52, 268-269.
Abstract:
A brief review is given on 3 articles published between 2002-2003 dealing with the prepn. of single-wall and multiple-wall C nanotubes and their possible applications.
BibTeX:
@article{Krueger2004,
author = {Krueger, Anke and Herges, Rainer.},
title = {Nanostructures and nanoarchitecture.},
journal = {Nachr. Chem.},
year = {2004},
volume = {52},
pages = {268-269}
}
Experimental and Theoretical Investigation of the Coarctate Cyclization of (2-Ethynylphenyl)phenyldiazenes.
L.D. Shirtcliff, T.J.R. Weakley, M.M. Haley, F. Koehler and R. Herges, J. Org. Chem. 2004, 69, 6979-6985.
Abstract:
A new route to substituted 2-phenyl-2H-indazoles through the cyclization of (2-ethynylphenyl)phenyldiazenes is presented. A coarctate reaction pathway forms the isoindazole carbene under neutral conditions, at moderate temps., and without the requirement of a carbene stabilizer. A wide variety of previously unknown diazene precursors was synthesized and cyclized. Trapping of the carbene with a silyl alc. followed by deprotection affords the 3-hydroxymethyl-2-phenyl-2H-indazoles in good overall yield. The free carbene could also be trapped as a [2 + 1] cycloadduct with 2,3-dimethyl-2-butene.
BibTeX:
@article{Shirtcliff2004,
author = {Shirtcliff, Laura D. and Weakley, Timothy J. R. and Haley, Michael M. and Koehler, Felix and Herges, Rainer.},
title = {Experimental and Theoretical Investigation of the Coarctate Cyclization of (2-Ethynylphenyl)phenyldiazenes.},
journal = {J. Org. Chem.},
year = {2004},
volume = {69},
pages = {6979-6985},
doi = {http://doi.org/10.1021/jo049011r%20S0022-3263(04)09011-5}
}
Metallocryptands: Arsenic-pi interactions stabilize a self-assembled As2L3 supramolecular complex.
W.J. Vickaryous, R. Herges and D.W. Johnson, Angew. Chem., Int. Ed. 2004, 43, 5831-5833.
Abstract:
An As2L3 (H2L = 4-HSCH2C6H4CH2SH) metallocryptand is the result of a new predictive design strategy for forming self-assembled supramol. As complexes. The assembly is remarkably stable to a variety of competing metal ions, harsh acid, and excess ligand. X-ray crystallog. studies and d. functional calcns. suggest that a strong As-pi interaction adds stability to the structure.
BibTeX:
@article{Vickaryous2004,
author = {Vickaryous, W. Jake and Herges, Rainer and Johnson, Darren W.},
title = {Metallocryptands: Arsenic-pi interactions stabilize a self-assembled As2L3 supramolecular complex.},
journal = {Angew. Chem., Int. Ed.},
year = {2004},
volume = {43},
pages = {5831-5833},
doi = {http://doi.org/10.1002/anie.200461011}
}
Synthesis of a Mobius aromatic hydrocarbon.
D. Ajami, O. Oeckler, A. Simon and R. Herges, Nature (London, U. K.) 2003, 426, 819-821.
Abstract:
The defining feature of arom. hydrocarbon compds. is a cyclic mol. structure stabilized by the delocalization of pi electrons that, according to the Hueckel rule, need to total 4n + 2 (n = 1,2,...); cyclic compds. with 4n pi electrons are antiarom. and unstable. But in 1964, Heilbronner predicted on purely theor. grounds that cyclic mols. with the topol. of a Moebius band-a ring constructed by joining the ends of a rectangular strip after having given one end half a twist-should be arom. if they contain 4n, rather than 4n + 2, pi electrons. The prediction stimulated attempts to synthesize Moebius arom. hydrocarbons, but twisted cyclic mols. are destabilized by large ring strains, with the twist also suppressing overlap of the p orbitals involved in electron delocalization and stabilization. In larger cyclic mols., ring strain is less pronounced but the structures are very flexible and flip back to the less-strained Hueckel topol. Although transition-state species, an unstable intermediate and a non-conjugated cyclic mol., all with a Moebius topol., have been documented, a stable arom. Moebius system has not yet been realized. Here we report that combining a normal' arom. structure (with p orbitals orthogonal to the ring plane) and a belt-like' arom. structure (with p orbitals within the ring plane) yields a Chen-Moebius compd. stabilized by its extended pi system.
BibTeX:
@article{Ajami2003,
author = {Ajami, D. and Oeckler, O. and Simon, A. and Herges, R..},
title = {Synthesis of a Mobius aromatic hydrocarbon.},
journal = {Nature (London, U. K.)},
year = {2003},
volume = {426},
pages = {819-821},
doi = {http://doi.org/10.1038/nature02224}
}
Pyrolysis of a Tubular Aromatic Compound.
M. Deichmann, C. Naether and R. Herges, Org. Lett. 2003, 5, 1269-1271.
Abstract:
In the attempt to close the walls of a small tubular system that is a substructure of a [4,4] armchair nanotube a very unusual rearrangement reaction was obsd.
BibTeX:
@article{Deichmann2003,
author = {Deichmann, M. and Naether, C. and Herges, Rainer.},
title = {Pyrolysis of a Tubular Aromatic Compound.},
journal = {Org. Lett.},
year = {2003},
volume = {5},
pages = {1269-1271},
doi = {http://doi.org/10.1021/ol034352x}
}
Synthesis of a chiral tube.
R. Herges, M. Deichmann, T. Wakita and Y. Okamoto, Angew. Chem., Int. Ed. 2003, 42, 1170-1172.
Abstract:
The alkylation of the rim of a tubelike structure leads to the formation of a chiral tube. Dimerized tetradehydrodianthracene was alkylated with tert-Bu chloride to give two compds., both octasubstituted picotubes. One product is chiral because it does not contain any symmetry element other than C4 and C2 symmetry axes. The other has C4h symmetry and is not chiral. These results may impact derivatization of larger carbon nanotubes in that alkylation can lead to well-defined products with increased soly., stability to further oxidn., and a redn. in the diam. of the opening of the tube.
BibTeX:
@article{Herges2003,
author = {Herges, Rainer and Deichmann, Markus and Wakita, Tsuneki and Okamoto, Yoshio.},
title = {Synthesis of a chiral tube.},
journal = {Angew. Chem., Int. Ed.},
year = {2003},
volume = {42},
pages = {1170-1172},
doi = {http://doi.org/10.1002/anie.200390308}
}
Computer-aided learning control in chemistry.
V. Pietzner and R. Herges, Math. Naturwiss. Unterr. 2003, 56, 356-364.
Abstract:
A background information for chem. teachers at advanced secondary schools is given on a new concept to design interactive, computer-aided learning controls. The concept is based on the topic addn. of bromine onto cyclopentene and the isomers of 2-butene. Psychol. basics of computer-aided learning are given. Yes/no-query, multiple choice, multiple select, completion exercise, and drag/drop-task are used as components. The evaluation of the concept involving students of chem. is reported.
BibTeX:
@article{Pietzner2003,
author = {Pietzner, Verena and Herges, Rainer.},
title = {Computer-aided learning control in chemistry.},
journal = {Math. Naturwiss. Unterr.},
year = {2003},
volume = {56},
pages = {356-364}
}
Picotube tetraanion: A novel lithiated tubular system.
N. Treitel, M. Deichmann, T. Sternfeld, T. Sheradsky, R. Herges and M. Rabinovitz, Angew. Chem., Int. Ed. 2003, 42, 1172-1176.
Abstract:
Title picotube with anthracenylidene units treated with alkali metal (Lithium) gave tetraanion which exhibited charge alternation encircling the 9,10 position. The optimized structure of lithiated tetraanion complex was corroborated by a comparison of the theor. calcd. and exptl. 13C NMR spectra.
BibTeX:
@article{Treitel2003,
author = {Treitel, Noach and Deichmann, Markus and Sternfeld, Tamar and Sheradsky, Tuvia and Herges, Rainer and Rabinovitz, Mordecai.},
title = {Picotube tetraanion: A novel lithiated tubular system.},
journal = {Angew. Chem., Int. Ed.},
year = {2003},
volume = {42},
pages = {1172-1176},
doi = {http://doi.org/10.1002/anie.200390309}
}
A tetrakis(secondary amide) derivative of norbornadiene: 7-isopropylidene-N,N',N'',N'''-tetraphenylnorborna-2,5-diene-2,3,5,6-tetracarboxamide.
T. Winkler, R. Herges, P.G. Jones and I. Dix, Acta Crystallogr., Sect. E: Struct. Rep. Online 2003, E59, o994-o996.
Abstract:
The title compd., C38H32N4O4, displays crystallog. 2-fold symmetry. Crystallog. data are given. The four amide groups are arranged such that four intramol. N-H...O H bonds are formed. The mols. are linked into chains by short C-H...O interactions involving the methine H atoms.
BibTeX:
@article{Winkler2003,
author = {Winkler, Torsten and Herges, Rainer and Jones, Peter G. and Dix, Ina.},
title = {A tetrakis(secondary amide) derivative of norbornadiene: 7-isopropylidene-N,N',N'',N'''-tetraphenylnorborna-2,5-diene-2,3,5,6-tetracarboxamide.},
journal = {Acta Crystallogr., Sect. E: Struct. Rep. Online},
year = {2003},
volume = {E59},
pages = {o994-o996},
doi = {http://doi.org/10.1107/S1600536803011346}
}
A tetrakis(secondary amide) derivative of quadricyclane: N,N',N'',N'''-tetraisopropyl-3-isopropylidenetetracyclo[3.2.0.02,7.04,6]heptane-1,5,6,7-tetracarboxamide.
T. Winkler, R. Herges, P.G. Jones and I. Dix, Acta Crystallogr., Sect. E: Struct. Rep. Online 2003, E59, o997-o999.
Abstract:
The title compd., C26H40N4O4, displays .apprx.2-fold symmetry. The four amide groups are arranged such that four intramol. N-H...O H bonds are formed. The mols. are linked into layers by bifurcated (C-H)2...O interactions. Crystallog. data are given.
BibTeX:
@article{Winkler2003a,
author = {Winkler, Torsten and Herges, Rainer and Jones, Peter G. and Dix, Ina.},
title = {A tetrakis(secondary amide) derivative of quadricyclane: N,N',N'',N'''-tetraisopropyl-3-isopropylidenetetracyclo[3.2.0.02,7.04,6]heptane-1,5,6,7-tetracarboxamide.},
journal = {Acta Crystallogr., Sect. E: Struct. Rep. Online},
year = {2003},
volume = {E59},
pages = {o997-o999},
doi = {http://doi.org/10.1107/S1600536803011358}
}
A tetrakis(secondary amide) derivative of quadricyclane: 3-isopropylidenetetracyclo[3.2.0.02,7.04,6]heptane-1,5,6,7-tetracarboxylic acid tetrakis(cyclohexylamide).
T. Winkler, R. Herges, P.G. Jones and I. Dix, Acta Crystallogr., Sect. E: Struct. Rep. Online 2003, E59, o1098-o1100.
Abstract:
The mol. of the title compd., C38H56N4O4, displays .apprx.2-fold symmetry. The four amide groups are arranged such that four intramol. N-H...O H bonds are formed. The mols. are linked into dimers by bifurcated (C-H)2...O interactions. Crystallog. data are given.
BibTeX:
@article{Winkler2003b,
author = {Winkler, Torsten and Herges, Rainer and Jones, Peter G. and Dix, Ina.},
title = {A tetrakis(secondary amide) derivative of quadricyclane: 3-isopropylidenetetracyclo[3.2.0.02,7.04,6]heptane-1,5,6,7-tetracarboxylic acid tetrakis(cyclohexylamide).},
journal = {Acta Crystallogr., Sect. E: Struct. Rep. Online},
year = {2003},
volume = {E59},
pages = {o1098-o1100},
doi = {http://doi.org/10.1107/S1600536803013692}
}
A tetrakis(tertiary amide) derivative of norbornadiene: 7-isopropylidenenorborna-2,5-diene-2,3,5,6-tetracarboxylic acid tetrakis(diethylamide).
T. Winkler, R. Herges, P.G. Jones and I. Dix, Acta Crystallogr., Sect. E: Struct. Rep. Online 2003, E59, o1101-o1102.
Abstract:
The mol. of the title compd., C30H48N4O4, displays .apprx.2-fold symmetry in the central part of the mol., but the Et groups depart from this symmetry. The carbonyl O atoms point alternately to different sides of the plane defined by the carbonyl C atoms. A three-dimensional H-bonding network is built up from five C-H...O interactions. Crystallog. data are given.
BibTeX:
@article{Winkler2003c,
author = {Winkler, Torsten and Herges, Rainer and Jones, Peter G. and Dix, Ina.},
title = {A tetrakis(tertiary amide) derivative of norbornadiene: 7-isopropylidenenorborna-2,5-diene-2,3,5,6-tetracarboxylic acid tetrakis(diethylamide).},
journal = {Acta Crystallogr., Sect. E: Struct. Rep. Online},
year = {2003},
volume = {E59},
pages = {o1101-o1102},
doi = {http://doi.org/10.1107/S1600536803013709}
}
A tetrakis(tertiary amide) derivative of quadricyclane: 3-isopropylidenetetracyclo[3.2.0.02,7.04,6]heptan-1,5,6,7-tetracarboxylic acid tetrakis(diethylamide).
T. Winkler, R. Herges, P.G. Jones and I. Dix, Acta Crystallogr., Sect. E: Struct. Rep. Online 2003, E59, o1103-o1105.
Abstract:
The title compd., C30H48N4O4, displays .apprx.2-fold symmetry in the central part of the mol., but the Et groups depart from this symmetry. The carbonyl O atoms point alternately to different sides of the plane defined by the carbonyl C atoms. Four C-H...O interactions link the mols. to form layers parallel to the bc plane. Crystallog. data are given.
BibTeX:
@article{Winkler2003d,
author = {Winkler, Torsten and Herges, Rainer and Jones, Peter G. and Dix, Ina.},
title = {A tetrakis(tertiary amide) derivative of quadricyclane: 3-isopropylidenetetracyclo[3.2.0.02,7.04,6]heptan-1,5,6,7-tetracarboxylic acid tetrakis(diethylamide).},
journal = {Acta Crystallogr., Sect. E: Struct. Rep. Online},
year = {2003},
volume = {E59},
pages = {o1103-o1105},
doi = {DOI: 10.1107/S1600536803013898}
}
A tetrakis(secondary amide) derivative of quadricyclane: 3-isopropylidenetetracyclo[3.2.0.02,7.04,6]heptane-1,5,6,7-tetracarboxylic acid tetrakis(tert-butylamide).
T. Winkler, R. Herges, P.G. Jones and I. Dix, Acta Crystallogr., Sect. E: Struct. Rep. Online 2003, E59, o1106-o1107.
Abstract:
The mol. of the title compd., C30H48N4O4, displays .apprx.2-fold symmetry. The four amide groups are arranged such that four intramol. N-H...O H bonds are formed. Crystallog. data are given.
BibTeX:
@article{Winkler2003e,
author = {Winkler, Torsten and Herges, Rainer and Jones, Peter G. and Dix, Ina.},
title = {A tetrakis(secondary amide) derivative of quadricyclane: 3-isopropylidenetetracyclo[3.2.0.02,7.04,6]heptane-1,5,6,7-tetracarboxylic acid tetrakis(tert-butylamide).},
journal = {Acta Crystallogr., Sect. E: Struct. Rep. Online},
year = {2003},
volume = {E59},
pages = {o1106-o1107},
doi = {http://doi.org/10.1107/S1600536803013904}
}
Synthesis, structure, and complexation properties of amide-substituted derivatives of norbornadiene and quadricyclane.
T. Winkler, I. Dix, P.G. Jones and R. Herges, Angew. Chem., Int. Ed. 2003, 42, 3541-3544.
Abstract:
Norbornadiene tetraamide (I) and quadricyclane tetraamide (II) were prepd. and their structures elucidated by x-ray anal. The complexation properties of I and II were investigated by the picrate extn. method. It was found that the Kex and Kass values for I are always higher than those for II. The crystal structure of I-NaSCN was also detd. to see whether all four carbonyl O's are available for coordination to a suitable cation.
BibTeX:
@article{Winkler2003f,
author = {Winkler, Torsten and Dix, Ina and Jones, Peter G. and Herges, Rainer.},
title = {Synthesis, structure, and complexation properties of amide-substituted derivatives of norbornadiene and quadricyclane.},
journal = {Angew. Chem., Int. Ed.},
year = {2003},
volume = {42},
pages = {3541-3544},
doi = {http://doi.org/10.1002/anie.200350959}
}
Synthesis and structure of bis-urea phenazines.
T. Fricke, A. Dickmans, U. Jana, M. Zabel, P.G. Jones, I. Dix, B. Konig and R. Herges, Z. Naturforsch., B: Chem. Sci. 2002, 57, 937-945.
Abstract:
Substituted phenazines I (R1 = R2 = H; R1 = CMe3, R2 = Me) with two urea units have been prepd. and characterized. X-ray structure analyses are reported for several prepd. compds., e.g. dinitrophenazine II. According to theor. calcns. the geometry of the two urea moieties in phenazines I should be well suited for the binding of trigonal planar anions, such as nitrate. NMR titrn. revealed that compd. I (R1 = CMe3, R2 = Me) indeed shows a weak interaction with nitrate ions in DMSO.
BibTeX:
@article{Fricke2002,
author = {Fricke, Tom and Dickmans, Anton and Jana, Umasish and Zabel, Manfred and Jones, Peter G. and Dix, Ina and Konig, Burkhard and Herges, Rainer.},
title = {Synthesis and structure of bis-urea phenazines.},
journal = {Z. Naturforsch., B: Chem. Sci.},
year = {2002},
volume = {57},
pages = {937-945},
url = {http://www.znaturforsch.com/ab/v57b/s57b0937.pdf}
}
Design of a neutral macrocyclic ionophore: synthesis and binding properties for nitrate and bromide anions.
R. Herges, A. Dikmans, U. Jana, F. Kohler, P.G. Jones, I. Dix, T. Fricke and B. Konig, Eur. J. Org. Chem. 2002, 3004-3014.
Abstract:
A macrocyclic neutral ionophore I capable of binding weakly coordinating anions such as nitrate and bromide in DMSO soln. has been designed by a stepwise, deductive approach. The optimum geometrical arrangement of the hydrogen bond donor sites in the target ionophore was detd. by d. functional theory (DFT) calcns. From these data, a suitable macrocyclic mol. framework was constructed. The 24-membered macrocyclic ionophore was synthesized by std. macrocyclization methods. NMR titrns. revealed mol. complexes with defined 1:1 stoichiometries in DMSO for I with nitrate, hydrogen sulfate, acetate, cyanide, iodide, and bromide ions, while dihydrogen phosphate, sulfate, and chloride ions yielded aggregates of higher stoichiometry. The nitrate binding consts. of I are substantial for a neutral ionophore with defined binding sites in pure DMSO soln. Bromide ions, which have a similar ion radius, are bound with an even higher affinity. Chloride is obviously too small, and iodine too large, to form 1:1 complexes. The binding motif of I was compared with related mols. of similar structure. As predicted from calcns., the small structural variations give rise to a complete loss of nitrate and bromide ion binding ability in DMSO. This sensitivity to geometrical changes and the affinity of I to nitrate and bromide ions, which are poor hydrogen bond acceptors, confirm the predicted complementarity of ionophore binding site and anion geometry. According to DFT and MD calcns. the higher affinity of I to bromide than to nitrate is mainly due to the greater flexibility of the bromide complex and thus to its higher entropy.
BibTeX:
@article{Herges2002,
author = {Herges, Rainer and Dikmans, Anton and Jana, Umasish and Kohler, Felix and Jones, Peter G. and Dix, Ina and Fricke, Tom and Konig, Burkhard.},
title = {Design of a neutral macrocyclic ionophore: synthesis and binding properties for nitrate and bromide anions.},
journal = {Eur. J. Org. Chem.},
year = {2002},
pages = {3004-3014},
doi = {http://doi.org/10.1002/1099-0690(200209)2002:17%3C3004::AID-EJOC3004%3E3.0.CO;2-O}
}
Two Unusual, Competitive Mechanisms for (2-Ethynylphenyl)triazene Cyclization: Pseudocoarctate versus Pericyclic Reactivity.
D.B. Kimball, R. Herges and M.M. Haley, J. Am. Chem. Soc. 2002, 124, 1572-1573.
Abstract:
The cyclization of (2-ethynylphenyl)triazenes in ODCB at 200 Deg gives exclusively cinnolines, whereas addn. of CuCl to 1,2-dichloroethane solns. of the triazenes at 50 Deg results in the sole formation of isoindazoles. DFT calcns. and D labeling studies suggest the intermediacy of a 3-dehydrocinnolinium ion, produced through a pericyclic transition state. Calcns. and trapping studies strongly implicate a carbene intermediate in isoindazole formation, which proceeds through a pseudocoarctate transition state.
BibTeX:
@article{Kimball2002,
author = {Kimball, David B. and Herges, Rainer and Haley, Michael M.},
title = {Two Unusual, Competitive Mechanisms for (2-Ethynylphenyl)triazene Cyclization: Pseudocoarctate versus Pericyclic Reactivity.},
journal = {J. Am. Chem. Soc.},
year = {2002},
volume = {124},
pages = {1572-1573},
doi = {http://doi.org/10.1021/ja017227u}
}
Deciphering the Mechanistic Dichotomy in the Cyclization of 1-(2-Ethynylphenyl)-3,3-dialkyltriazenes: Competition between Pericyclic and Pseudocoarctate Pathways.
D.B. Kimball, T.J.R. Weakley, R. Herges and M.M. Haley, J. Am. Chem. Soc. 2002, 124, 13463-13473.
Abstract:
The mechanistic aspects of the cyclization of (2-ethynylphenyl)triazenes under both thermal and Cu-mediated conditions are reported. For cyclization to an isoindazole, a carbene mechanistic pathway is proposed. The carbene intermediate can react with O, dimerize to give an alkene, or be trapped either intermolecularly (using 2,3-dimethyl-2-butene to generate a cyclopropane) or intramolecularly (using a biphenyl moiety at the terminus of the acetylene to form a fluorene). D.-functional theory (DFT) calcns. support a pseudocoarctate pathway for this type of cyclization. Thermal cyclization to give a cinnoline from (2-ethynylphenyl)triazenes probably occurs through a pericyclic pathway. DFT calcns. predict a zwitterionic dehydrocinnolinium intermediate that is supported by D trapping studies as well as cyclizations performed using a 2,2,6,6-tetramethylpiperidine moiety at the 3-position of the triazene.
BibTeX:
@article{Kimball2002a,
author = {Kimball, David B. and Weakley, Timothy J. R. and Herges, Rainer and Haley, Michael M.},
title = {Deciphering the Mechanistic Dichotomy in the Cyclization of 1-(2-Ethynylphenyl)-3,3-dialkyltriazenes: Competition between Pericyclic and Pseudocoarctate Pathways.},
journal = {J. Am. Chem. Soc.},
year = {2002},
volume = {124},
pages = {13463-13473},
doi = {http://doi.org/10.1021/ja027809r%20S0002-7863(02)07809-5}
}
Homoaromaticity in tris(ethylene)nickel(0) and tris(ethyne)nickel(0).
R. Herges and A. Papafilippopoulos, Angew. Chem., Int. Ed. 2001, 40, 4671-4674.
Abstract:
The authors have now found a surprisingly strong cyclic homoconjugation between the ethylene units in the planar structure of tris(ethylene)nickel(0) (1a) and between the ethyne ligands in the D3 structure of tris(ethyne)nickel(0) (2a). The C...C distance between the ligands of 2.681 .ANG. in 1a and 2.703 .ANG. in 2a is in each case far below the sum of the van der Waals radii of the neighboring sp2 and sp C atoms. Thus, 1a and 2a can be designated to be arom. or on the way to trimerizing to cyclohexane and benzene, resp. This does not only explain the preference of the planar arrangement of the fragments in tris(ethylene)nickel(0) but also sheds light upon the role of Ni(0) as a catalyst in C-C bond formation processes. The authors' results among other methods are based on a recently published method for the study of delocalization and conjugation effects in mols. This ACID (anisotropy of the induced c.d.) method provides a powerful and general way to visualize the d. of delocalized electrons and to quantify conjugation effects.
BibTeX:
@article{Herges2001,
author = {Herges, Rainer and Papafilippopoulos, Andrea.},
title = {Homoaromaticity in tris(ethylene)nickel(0) and tris(ethyne)nickel(0).},
journal = {Angew. Chem., Int. Ed.},
year = {2001},
volume = {40},
pages = {4671-4674},
doi = {http://doi.org/10.1002/1521-3773(20011217)40:24%3C4671::AID-ANIE4671%3E3.0.CO;2-T}
}
Delocalization of Electrons in Molecules.
R. Herges and D. Geuenich, J. Phys. Chem. A 2001, 105, 3214-3220.
Abstract:
We report a general method for the investigation and quantification of delocalization in mols. The method is based on the anisotropy of the current-induced d. (ACID). Compared to the c.d., which has been frequently used to investigate delocalization, the ACID approach has several advantages: it is a scalar field which is invariant with respect to the relative orientation of the magnetic field and the mol., it is not a simple function of the overall electron d., it has the same symmetry as the wave function, and it can be plotted as an isosurface. Several selected examples demonstrate the predictive power and the general applicability of this method.
BibTeX:
@article{Herges2001a,
author = {Herges, Rainer and Geuenich, Daniel.},
title = {Delocalization of Electrons in Molecules.},
journal = {J. Phys. Chem. A},
year = {2001},
volume = {105},
pages = {3214-3220},
doi = {http://doi.org/10.1021/jp0034426%20S1089-5639(00)03442-3}
}
Alkali metal cation selectivity of an oligo-ether substituted norbornadiene and quadricyclane isomer.
R. Herges and T. Winkler, Eur. J. Org. Chem. 2001, 4419-4422.
Abstract:
The paper presents investigations aimed at using the norbornadiene/quadricyclane system as a framework for a switchable cation carrier. According to mol. modeling studies a suitably substituted system should perform a pincer-like motion upon isomerization and reisomerization, while complexing and decomplexing a host mol. To this end, the authors studied the complexing abilities of a 1,5,6,7-tetrasubstituted quadricyclane polyether and its corresponding norbornadiene isomer. The picrate extn. method was applied to det. the extn. consts. Kex and the assocn. consts. Kass of these polyethers with alkali metal cations in chloroform. As expected, the complexes of the quadricyclane polyether with Li+, Na+, K+ and Cs+ are more stable than those of the norbornadiene isomer. This difference reaches a max. for potassium. The interconversion between the norbornadiene polyether and the corresponding quadricyclane was also examd. The norbornadiene can be converted photochem. to the quadricyclane with 50 % conversion while the reverse reaction is catalyzed by neutral aluminum oxide in 71 % yield. No byproduct was detected in either of the isomerization reactions.
BibTeX:
@article{Herges2001b,
author = {Herges, Rainer and Winkler, Torsten.},
title = {Alkali metal cation selectivity of an oligo-ether substituted norbornadiene and quadricyclane isomer.},
journal = {Eur. J. Org. Chem.},
year = {2001},
pages = {4419-4422},
doi = {http://doi.org/10.1002/1099-0690(200112)2001:23%3C4419::AID-EJOC4419%3E3.0.CO;2-C}
}
Ethynylogization of a coarctate fragmentation.
R. Herges, D. Geuenich, G. Bucher and C. Tonshoff, Chem.--Eur. J. 2000, 6, 1224-1228.
Abstract:
Coarctate reactions form a sep. class of elementary closed-shell processes in addn. to polar and pericyclic reactions. Hence, they also follow a different homol. principle. Whereas vinylogous polar and pericyclic reactions differ in the length of the reacting system by a double bond, coarctate reactions can be homologized (ethynylogized) by extending a known system by a triple bond. The prediction, which is based on theor. considerations, is confirmed exptl. by the fragmentation of cyclopropylethynyl nitrene to cyanoacetylene and ethylene, a reaction that is "ethynyloguous" to the known fragmentation of cyclopropyl nitrene to ethylene and HCN.
BibTeX:
@article{Herges2000,
author = {Herges, Rainer and Geuenich, Daniel and Bucher, Gotz and Tonshoff, Christina.},
title = {Ethynylogization of a coarctate fragmentation.},
journal = {Chem.--Eur. J.},
year = {2000},
volume = {6},
pages = {1224-1228},
doi = {http://doi.org/10.1002/(SICI)1521-3765(20000403)6:7%3C1224::AID-CHEM1224%3E3.0.CO;2-H}
}
A highly correlated conformational motion of a tube-like fully conjugated hydrocarbon.
R. Herges, M. Deichmann, J. Grunenberg and G. Bucher, Chem. Phys. Lett. 2000, 327, 149-152.
Abstract:
By comparing the matrix IR spectrum (Ar, 12 K) with theor. calcd. spectra (B3LYP/6-31G*), the structure of the tube-like hydrocarbon I has been detd. to be a fast equil. of two D2d sym. structures. The previously assumed higher sym. D4h structure was found to be the transition state of this conformational interconversion. The conformational process involves the correlated and simultaneous pincer-like movement of the four relatively rigid anthracene units. Two pincers are always closed and two are open. Changing the state of one of the pincers reverses the state of the other three pincers. Upon suitable substitution, the mol. framework meets the requirements to be used as a logic gate.
BibTeX:
@article{Herges2000a,
author = {Herges, R. and Deichmann, M. and Grunenberg, J. and Bucher, G.},
title = {A highly correlated conformational motion of a tube-like fully conjugated hydrocarbon.},
journal = {Chem. Phys. Lett.},
year = {2000},
volume = {327},
pages = {149-152},
doi = {http://doi.org/10.1016/S0009-2614(00)00869-1}
}
Quadricyclane radical cation isomerizations.
R. Herges, F. Starck, T. Winkler and M. Schmittel, Chem.--Eur. J. 1999, 5, 2965-2970.
Abstract:
Isopropylidenequadricyclane I (R = MeOCH2, MeOCH2CH2OCH2) upon oxidn. with catalytic amts. of the electron transfer catalyst tris(p-tolyl)aminium hexafluoroantimonate (TTA.+ SbF6-) gives bicycloheptadiene II spontaneously and in quant. yields. Epoxidn. of the isopropylidene group drastically changes the reactivity of the quadricyclane framework. Under the same reaction conditions (catalytic amts. of TTA.+ SbF6-) norbornadiene III is formed spontaneously and quant. according to an NMR study. Theor. calcns. on the unsubstituted model quadricyclane and isopropylidenequadricyclane at the B3LYP/3-21G and MP2/3-21G level of d. functional theory (DFT) and ab initio theory reveal the mechanism of both reactions. In the parent quadricyclane system the concerted (but not synchronous) three-electron cycloreversion is favored, and by hyperconjugation with the pi* orbital the isopropylidene deriv. prefers a simultaneous cleavage of a "lateral" bond and a cyclobutane bond to give a radical cation intermediate. Starting from the intermediate there are two pathways to the product bicycloheptadiene (II; R = H) (IV). The pathway involving a trimethylenemethane intermediate turns out to be a dead end because the system has to overcome a very high activation barrier to give the bicycloheptadiene. Much more favorable and consistent with the reaction conditions is a 1,2-shift, which has a barrier of only 1.7 kcal mol-1, leading directly to a bicycloheptadiene radical cation and subsequently upon redn. to the neutral product IV. A no. of known quadricyclane rearrangements can be explained by these mechanisms.
BibTeX:
@article{Herges1999,
author = {Herges, Rainer and Starck, Felix and Winkler, Torsten and Schmittel, Michael.},
title = {Quadricyclane radical cation isomerizations.},
journal = {Chem.--Eur. J.},
year = {1999},
volume = {5},
pages = {2965-2970},
doi = {http://doi.org/10.1021/ol034352x%20S1523-7060(03)04352-9}
}
Synthesis of photoresponsive polyethers. [Erratum to document cited in CA130:66213].
F. Starck, P.G. Jones, R. Herges and T. Winkler, Eur. J. Org. Chem. 1999, 361.
Abstract:
The name of an addnl. author (T. Winkler) is added. The elemental anal. data of several compds. were inadvertently omitted and should be added as follows: 3c: C18H28O4 (308.2): calcd. C 70.10, H 9.15; found C 69.43, H 9.16; 4c: C26H44O8 (484.3): calcd. C 64.44, H 9.15; found C 64.68, H 9.33; 5c: C18H28O4 (308.2): calcd. C 70.10, H 9.15; found C 69.95, H 9.28.
BibTeX:
@article{Starck1999,
author = {Starck, Felix and Jones, Peter G. and Herges, Rainer and Winkler, T.},
title = {Synthesis of photoresponsive polyethers. [Erratum to document cited in CA130:66213].},
journal = {Eur. J. Org. Chem.},
year = {1999},
pages = {361},
doi = {http://doi.org/10.1002/(SICI)1099-0690(199901)1999:1%3C361::AID-EJOC361%3E3.0.CO;2-E}
}
Long-lived [1.1.1.1]- and [2.2.1.1]-'Isopagodane' dications: novel 4C/2e s-bishomoaromatic dications.
G.K. Surya Prakash, K. Weber, G.A. Olah, K. Weber, H. Prinzbach, M. Wollenweber, M. Etzkorn, T. Voss and R. Herges, Chem. Commun. (Cambridge) 1999, 1029-1030.
Abstract:
The dications generated from [1.1.1.1]- and [2.2.1.1]isopagodane I (n = 1 and 2, resp.) in SbF5-SO2ClF soln. at -78 DegC are of s-bishomoarom. nature (4C/2e), very similar in geometry, yet chem. different in their properties.
BibTeX:
@article{SuryaPrakash1999,
author = {Surya Prakash, G. K. and Weber, Klaus and Olah, George A. and Weber, Klaus and Prinzbach, Horst and Wollenweber, Markus and Etzkorn, Markus and Voss, Torsten and Herges, Rainer.},
title = {Long-lived [1.1.1.1]- and [2.2.1.1]-'Isopagodane' dications: novel 4C/2e s-bishomoaromatic dications.},
journal = {Chem. Commun. (Cambridge)},
year = {1999},
pages = {1029-1030},
doi = {http://doi.org/10.1039/a901202h}
}
A spontaneous fragmentation: from the Criegee zwitterion to coarctate Mobius aromaticity.
C. Berger, C. Bresler, U. Dilger, D. Geuenich, R. Herges, H. Rottele and G. Schroder, Angew. Chem., Int. Ed. 1998, 37, 1850-1853.
Abstract:
Spiroozonides [4,5,7-trioxaspiro[2.4]heptanes (e.g., I) and -hept-1-enes], formed by the reaction of cyclopropanones or cyclopropenones with formaldehyde O-oxide, decompd. spontaneously to CO2, CH2O, and the corresponding alkene or alkyne; their fragmentation fulfilled the criteria for reactions with a coarctate transition state (in which two bonds are simultaneously formed and broken at one or more atoms). Topol. anal. shows that the 8-electron concerted transition state is stabilized by coarctate Mobius aromaticity.
BibTeX:
@article{Berger1998,
author = {Berger, Christian and Bresler, Christian and Dilger, Ulrich and Geuenich, Daniel and Herges, Rainer and Rottele, Herbert and Schroder, Gerhard.},
title = {A spontaneous fragmentation: from the Criegee zwitterion to coarctate Mobius aromaticity.},
journal = {Angew. Chem., Int. Ed.},
year = {1998},
volume = {37},
pages = {1850-1853},
doi = {http://doi.org/10.1002/(SICI)1521-3773(19980803)37:13/14%3C1850::AID-ANIE1850%3E3.0.CO;2-B}
}
Thermal behavior of spiroozonides from formaldehyde-O-oxide and tropone derivatives: a coarctate reaction.
C. Berger, S. Dieterich, U. Dilger, D. Feuenich, H. Helios, R. Herges, P. Kirchmer, H. Rottele and G. Schroder, Angew. Chem., Int. Ed. 1998, 37, 1854-1857.
Abstract:
Spiroozonides I (R1 = e.g., H, alkyl, Ph, MeO, halo; R2 = H, Ph, t-Bu), formed in the reaction of the corresponding tropones with formaldehyde O-oxide, undergo fragmentation to arom. leaving groups (1-R1-2-R2-benzene), CO2, and formaldehyde. DFT calcns. indicated that the rate-detg. step is not the coarctate fragmentation, but rather the electrocyclic ring closure to norcaradiene that precedes fragmentation. A potential energy surface for the fragmentation of the parent I (R1 = R2 = H) was given, including the intermediate diastereomeric norcaradienes. Substituent effects on fragmentation kinetics were attributed to steric factors that affect the cycloheptatriene/norcaradiene isomerization.
BibTeX:
@article{Berger1998a,
author = {Berger, Christian and Dieterich, Stefan and Dilger, Ulrich and Feuenich, Daniel and Helios, Heike and Herges, Rainer and Kirchmer, Peter and Rottele, Herbert and Schroder, Gerhard.},
title = {Thermal behavior of spiroozonides from formaldehyde-O-oxide and tropone derivatives: a coarctate reaction.},
journal = {Angew. Chem., Int. Ed.},
year = {1998},
volume = {37},
pages = {1854-1857},
doi = {http://doi.org/10.1002/(SICI)1521-3773(19980803)37:13/14%3C1854::AID-ANIE1854%3E3.0.CO;2-O}
}
Formaldehyde O-oxide and colchicine. An elegant route to the allocolchicines.
U. Dilger, B. Franz, H. Roettele, G. Schroeder and R. Herges, J. Prakt. Chem./Chem.- Ztg. 1998, 340, 468-471.
Abstract:
Reactions of formaldehyde O-oxide with colchicine and its derivs. under O3-free conditions are reported. The fragmentation of intermediately formed spiro ozonides opens up an elegant route to allocolchicines. The fragmentation kinetics are described.
BibTeX:
@article{Dilger1998,
author = {Dilger, Ulrich and Franz, Baerbel and Roettele, Herbert and Schroeder, Gerhard and Herges, Rainer.},
title = {Formaldehyde O-oxide and colchicine. An elegant route to the allocolchicines.},
journal = {J. Prakt. Chem./Chem.- Ztg.},
year = {1998},
volume = {340},
pages = {468-471},
doi = {http://doi.org/10.1002/prac.19983400510}
}
[2.2.2.2]Pagodane: Synthesis and Oxidation of Nonclassical Valence-Isomeric 4C/3e and s-Bishomoaromatic 4C/2e Ions.
M. Etzkorn, F. Wahl, M. Keller, H. Prinzbach, F. Barbosa, V. Peron, G. Gescheidt, J. Heinze and R. Herges, J. Org. Chem. 1998, 63, 6080-6081.
Abstract:
The existence of a [2.2.2.2]pagodane-derived s-bishomoarom. dication was demonstrated using electron nuclear double resonance and ESR spectroscopy.
BibTeX:
@article{Etzkorn1998,
author = {Etzkorn, Markus and Wahl, Fabian and Keller, Manfred and Prinzbach, Horst and Barbosa, Frederique and Peron, Vincent and Gescheidt, Georg and Heinze, Juergen and Herges, Rainer.},
title = {[2.2.2.2]Pagodane: Synthesis and Oxidation of Nonclassical Valence-Isomeric 4C/3e and s-Bishomoaromatic 4C/2e Ions.},
journal = {J. Org. Chem.},
year = {1998},
volume = {63},
pages = {6080-6081},
doi = {http://doi.org/10.1021/jo980892+}
}
Straightforward syntheses of biradical-producing bicyclic dienediynes -- dienediyne ketones cycloaromatize via the Saito-Myers and not via the neocarzinostatin pathway.
F. Ferri, R. Bruckner and R. Herges, New J. Chem. 1998, 22, 531-546.
Abstract:
The dienediyne models I and II of the pharmacophore of the antitumor natural product neocarzinostatin were prepd. Each synthesis required six steps from alpha -formylcyclohexanone. The approach used two key steps; the first consisted of one-pot biscoupling reactions between propargyl alc., 2,2-dimethyl-3-butyn-1-ol and the bis(enoltrifluoromethanesulfonate). The second key step corresponded to ring-closing pinacol coupling reactions of the dialdehydes corresponding to I and II. The dienediyne models I and II cycloaromatized efficiently when treated with Me thioglycolate and 1,4-cyclohexadiene at 25 DegC via a Saito-Myers cyclization (yielding octahydroanthracenones and octahydrophenanthrenones); in addn., compds. tentatively assigned as octahydrobenzazulenones from a competing Schmittel cyclization were isolated. According to d. functional theory (B3LYP/6-31G*) and ab initio calcns. [CASMP2(2.2)/6-31G//CAS(2.2)/6-31G], the core structures of the octahydroanthracenones and octahydrophenanthrenones obtained form via the Saito-Myers cyclization of enyneallenyl ketones to toluene-alpha ,meta biradicals not via neocarzinostatin-like cycloaromatizations of the tautomeric enyne[3]cumulenols to styrene alpha ,meta-biradicals. The two cyclization modes were predicted to have similar activation barriers (Saito-Myers: 16.0 kcal mol-1; neocarzinostatin type: 18.3 kcal mol-1) but, the enyneallenyl ketone was a much more stable (21.1 kcal mol-1) cycloaromatization substrate than the enynecumulenol.
BibTeX:
@article{Ferri1998,
author = {Ferri, Fabiola and Bruckner, Reinhard and Herges, Rainer.},
title = {Straightforward syntheses of biradical-producing bicyclic dienediynes -- dienediyne ketones cycloaromatize via the Saito-Myers and not via the neocarzinostatin pathway.},
journal = {New J. Chem.},
year = {1998},
volume = {22},
pages = {531-546},
doi = {http://doi.org/10.1039/a709205i}
}
Straightforward synthesis of biradical-producing bicycle dienediynes--dienediyne ketones cycloaramatize via the Saito-Myers and not via the neocarzinostatin pathway. [Erratum to document cited in CA129:95337].
F. Ferri, R. Bruckner and R. Herges, New J. Chem. 1998, 22, 649.
Abstract:
In Scheme 5, there is a double bond missing in the structure of 23. In Table 1, a S atom was erroneously drawn as a CH2 group in the structure of 30/iso-30. The correct structures are given.
BibTeX:
@article{Ferri1998a,
author = {Ferri, Fabiola and Bruckner, Reinhard and Herges, Rainer.},
title = {Straightforward synthesis of biradical-producing bicycle dienediynes--dienediyne ketones cycloaramatize via the Saito-Myers and not via the neocarzinostatin pathway. [Erratum to document cited in CA129:95337].},
journal = {New J. Chem.},
year = {1998},
volume = {22},
pages = {649}
}
Molecular modeling. Methods and programs.
J. Grunenberg and R. Herges, Nachr. Chem., Tech. Lab. 1998, 46, A28-A30,A32,A34-A37.
Abstract:
A review with 47 refs., describing principles of mol. modeling and the theor. models mol. mechanics (force field) and quantum mechanics (MO methods) combined in computer chem., is added. Computer programs for mol. modeling including the methods are listed.
BibTeX:
@article{Grunenberg1998,
author = {Grunenberg, Joerg and Herges, Rainer.},
title = {Molecular modeling. Methods and programs.},
journal = {Nachr. Chem., Tech. Lab.},
year = {1998},
volume = {46},
pages = {A28-A30,A32,A34-A37}
}
A silver(I) complex of a tube-shaped hydrocarbon.
S. Kammermeier, P.G. Jones, I. Dix and R. Herges, Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1998, C54, 1078-1081.
Abstract:
The bis[silver(I) trifluoromethanesulfonate] complex of the fully conjugated tubelike hydrocarbon 5,24:6, 11:12,17:18,23-tetra[1,2]benzenotetrabenzo[a,e,i,m]cyclohexadecene crystallizes with two mols. of H2O and two of toluene, and thus has the formula [Ag2(C56H32)(C7H8)2(H2O)2](CF3SO3)2. The formula unit of the latter displays inversion symmetry, while the ligand itself displays approx. D4h symmetry. Each Ag+ ion is coordinated by one C atom of each of two adjacent rings of the ligand, one H2O O and one toluene C-C bound. Crystallog. data are given.
BibTeX:
@article{Kammermeier1998,
author = {Kammermeier, Stefan and Jones, Peter G. and Dix, Ina and Herges, Rainer.},
title = {A silver(I) complex of a tube-shaped hydrocarbon.},
journal = {Acta Crystallogr., Sect. C: Cryst. Struct. Commun.},
year = {1998},
volume = {C54},
pages = {1078-1081},
doi = {http://doi.org/10.1107/S0108270198002406}
}
Matrix isolation of 3,4-benzocyclodeca-3,7,9-triene-1,5-diyne.
C. Koetting, W. Sander, S. Kammermeier and R. Herges, Eur. J. Org. Chem. 1998, 799-803.
Abstract:
3,4-Benzocyclodeca-3,7,9-triene-1,5-diyne was synthesized from two different precursors and characterized by matrix-isolation spectroscopy. Energies, structure, and IR spectra of the product, the intermediate 9,10-didehydroanthracene, and of the transition state of the Bergman cyclization were calcd. at the B3LYP/6-31G* level of theory.
BibTeX:
@article{Koetting1998,
author = {Koetting, Carsten and Sander, Wolfram and Kammermeier, Stefan and Herges, Rainer.},
title = {Matrix isolation of 3,4-benzocyclodeca-3,7,9-triene-1,5-diyne.},
journal = {Eur. J. Org. Chem.},
year = {1998},
pages = {799-803},
doi = {http://doi.org/10.1002/(SICI)1099-0690(199805)1998:5%3C799::AID-EJOC799%3E3.0.CO;2-G}
}
Synthesis of photoresponsive polyethers.
F. Starck, P.G. Jones and R. Herges, Eur. J. Org. Chem. 1998, 2533-2539.
Abstract:
A Diels-Alder/retro Diels-Alder sequence provides access to 2,3,5-tri- and 2,3,5,6-tetracarboxylate-substituted norbornadienes. Attempts to reduce the norbornadiene esters with LiAlH4 failed. The corresponding quadricyclanes, which are available by photoisomerization of the norbornadienes give the alcs. in 32 and 74% yield. The quadricyclane alcs. I (R = H with R1, R2 = H; R1 = H, R2 = CH2OH; R1, R2 = CH2OH) are converted with MeI to the corresponding ethers or with 4-MeC6H4SO3(CH2)OMe to the "tentacle mols." I [R = (CH2)2OMe with R1, R2 = H; R1 = H, R2 = CH2O(CH2)2OMe; R1, R2 = CH2O(CH2)2OMe]. A no. of catalysts were tested to reisomerize the "tentacle" quadricyclanes to the corresponding norbornadienes. Neutral Al2O3 proved to be most effective. In preliminary studies, the tentacle quadricyclanes exhibit excellent complexing properties for Na+ and K+, whereas the norbornadiene isomers are less effective complexing agents.
BibTeX:
@article{Starck1998,
author = {Starck, Felix and Jones, Peter G. and Herges, Rainer.},
title = {Synthesis of photoresponsive polyethers.},
journal = {Eur. J. Org. Chem.},
year = {1998},
pages = {2533-2539},
doi = {http://doi.org/10.1002/(SICI)1099-0690(199811)1998:11%3C2533::AID-EJOC2533%3E3.0.CO;2-Q}
}
Spectroscopic detection and theoretical studies of a 2:1 bromine-olefin pi complex.
R. Bianchini, C. Chiappe, D. Lenoir, P. Lammen, R. Herges and J. Grunenberg, Angew. Chem., Int. Ed. Engl. 1997, 36, 1284-1287.
Abstract:
The UV spectrum of the 2:1 Br2-tetraneopentylethylene (TNPE) complex was recorded under conditions of high Br2 excess by subtracting out the pure Br2 contribution. The enthalpy of formation of the 2:1 complex, i.e., TNPE.Br2 + Br2 -> TNPE.2Br2, was -1.6 kcal/mol; the small entropic factor Delta S = -6.1 cal mol-1 K-1 was attributed to the large degree of conformational freedom of the second Br2 mol. DFT and ab initio MP2 structural data on model 1:1 and 2:1 Br2-ethylene complexes and on (Br2)2 dimers were reported. The most stable 1:1 complex was the T-type. Two structure min. were located for the 2:1 complex: in one, both sides of the ethene pi system interact with bromine (Br2.olefin.Br2), and in the second, the second bromine is bound to the first bromine (Br2.Br2.olefin) with collinear arrangement of the midpoint of the C:C bond, the two Br atoms of the first Br2, and one Br atom of the second Br2. Taking account of steric hindrance, the Br2.Br2.olefin structure should be favored relative to Br2.olefin.Br2 by about 1.4 kcal/mol. The deviation of theor. and exptl. values for the formation enthalpy of the 2:1 complex was attributed to Br2 dimerization and; for the reaction olefin + (Br2)2 -> 2:1 complex theory and expt. are in agreement.
BibTeX:
@article{Bianchini1997,
author = {Bianchini, Roberto and Chiappe, Cinzia and Lenoir, Dieter and Lammen, Peter and Herges, Rainer and Grunenberg, Jorg.},
title = {Spectroscopic detection and theoretical studies of a 2:1 bromine-olefin pi complex.},
journal = {Angew. Chem., Int. Ed. Engl.},
year = {1997},
volume = {36},
pages = {1284-1287},
doi = {http://doi.org/10.1002/anie.199712841}
}
From cyclobutane (four-center/three-electron) radical cations to the Mills-Nixon effect.
G. Gescheidt, H. Prinzbach, A.G. Davies and R. Herges, Acta Chem. Scand. 1997, 51, 174-180.
Abstract:
A review with 49 refs. One-electron oxidn. of pagodane-type mols. led to rather unusual radical cations. The corresponding ESR spectra were interpreted in terms of 2 different forms of 4-center/3-electron radical cations being embedded inside rigid polycyclic skeletons. Quantum-mech. calcns. assigned these 2 forms to an 'extended' and to a 'tight' structure representing 2 stages on the (D2h) reaction coordinate of a [2+1] cycloaddn. A cyclobutane moiety changed the ordering of the 2 highest occupied orbitals in the radical cation of an alternant hydrocarbon. This unexpected observation on the radical cation of binaphthylene was traced back to the Mills-Nixon effect introduced in 1930.
BibTeX:
@article{Gescheidt1997,
author = {Gescheidt, Georg and Prinzbach, Horst and Davies, Alwyn G. and Herges, Rainer.},
title = {From cyclobutane (four-center/three-electron) radical cations to the Mills-Nixon effect.},
journal = {Acta Chem. Scand.},
year = {1997},
volume = {51},
pages = {174-180},
doi = {http://doi.org/10.3891/acta.chem.scand.51-0174}
}
Calculation of molecular vibrations: selective scaling factors for semiempirical force constants.
J. Grunenberg and R. Herges, J. Comput. Chem. 1997, 18, 2050-2059.
Abstract:
The complete force const. matrixes of a set of 50 aliph. and arom. hydrocarbons are calcd. at the d. functional theory B3LYP/6-31 + G(d, p) and semiempirical PM3 levels of theory. After transformation from Cartesian to nonredundant internal coordinates, the errors in the semiempirical force consts. are systematically analyzed. The force consts. of the C-C stretching coordinates can be easily cor. by a second-order fit. Thus, only two parameters are needed to reduce the mean error from 21.2 to 1.23%. The errors of other internal coordinates, particularly those including torsional modes, exhibit a larger diversity. The performance of the correction scheme in predicting vibrational spectra is shown for several examples including buckminsterfullerene (C60).
BibTeX:
@article{Grunenberg1997,
author = {Grunenberg, J. and Herges, R..},
title = {Calculation of molecular vibrations: selective scaling factors for semiempirical force constants.},
journal = {J. Comput. Chem.},
year = {1997},
volume = {18},
pages = {2050-2059},
doi = {http://doi.org/10.1002/(SICI)1096-987X(199712)18:16%3C2050::AID-JCC9%3E3.0.CO;2-K}
}
Introduction to Theoretical Organic Chemistry and Molecular Modeling by W. B. Smith.
R. Herges, Angew. Chem., Int. Ed. Engl. 1997, 36, 1355.
BibTeX:
@article{Herges1997,
author = {Herges, Rainer.},
title = {Introduction to Theoretical Organic Chemistry and Molecular Modeling by W. B. Smith.},
journal = {Angew. Chem., Int. Ed. Engl.},
year = {1997},
volume = {36},
pages = {1355},
doi = {http://doi.org/10.1002/anie.199713551}
}
[2 + 2] Cycloaddition products of tetradehydrodianthracene: experimental and theoretical proof of extraordinary long C-C single bond.
S. Kammermeier, P.G. Jones and R. Herges, Angew. Chem., Int. Ed. Engl. 1997, 36, 1757-1760.
Abstract:
Cycloaddn. products I and II were characterized by x-ray structure anal. The central C(1)-C(2) single bond in I is 1.677(3) .ANG. and the corresponding bond in II is even longer, 1.713(2) .ANG.. The extraordinary bond length may be explained by the interplay of three factors: (1)through-bond interaction(pi-s*) of the four benzene rings with the C-C single bond; (2) the strain induced by the facing, strongly pyramidalized double bond, and (3) the ring strain of the cyclobutene or benzocyclobutene ring. Exptly. detd. and calcd (B3LYP/6-31G* and PM3) bond lengths of the central single C-C bond in selected anthracenes were given.
BibTeX:
@article{Kammermeier1997,
author = {Kammermeier, Stefan and Jones, Peter G. and Herges, Rainer.},
title = {[2 + 2] Cycloaddition products of tetradehydrodianthracene: experimental and theoretical proof of extraordinary long C-C single bond.},
journal = {Angew. Chem., Int. Ed. Engl.},
year = {1997},
volume = {36},
pages = {1757-1760},
doi = {http://doi.org/10.1002/anie.199717571}
}
Belt-like aromatic hydrocarbons by metathesis reaction with tetradehydrodianthracene.
S. Kammermeier, P.G. Jones and R. Herges, Angew. Chem., Int. Ed. Engl. 1997, 36, 2200-2202.
Abstract:
Fully conjugated belt-like or tube-like arom. hydrocarbons can be regarded as structures in which the pi-electron system is spherically deformed by the introduction of bridging ligands. The synthesis of a small belt-like, fully conjugated system was reported via ring enlargement by metathesis of tetradehydrodianthracene.
BibTeX:
@article{Kammermeier1997a,
author = {Kammermeier, Stefan and Jones, Peter G. and Herges, Rainer.},
title = {Belt-like aromatic hydrocarbons by metathesis reaction with tetradehydrodianthracene.},
journal = {Angew. Chem., Int. Ed. Engl.},
year = {1997},
volume = {36},
pages = {2200-2202},
doi = {http://doi.org/10.1002/anie.199722001}
}
Diels-Alder reactions of tetradehydrodianthracene with electron-deficient dienes.
J. Sauer, J. Breu, U. Holland, R. Herges, H. Neumann and S. Kammermeier, Liebigs Ann./Recl. 1997, 1473-1479.
Abstract:
Theor. calcns. and simple MO considerations predict that a coplanar and spatially close arrangement of double bonds in structures such as dehydrodianthracene I, should both lower the LUMO and raise the HOMO energy of the pi system. Thus the reactivity in Diels-Alder reactions towards electron-rich and electron-deficient dienes should be enhanced. The first effect has already been shown in a previous paper, the latter statement is now also confirmed by the reactivity of I in Diels-Alder reactions with inverse electron demand. In [4+2] cycloaddn. reactions of I with 1,2,4,5-tetrazines II (R = H, Me, CO2Me, CF3) the electronic effect of 3,6-substituents in tetrazines is far outweighed by steric factors resulting in an unexpected reactivity sequence: H .mchgt. Me   CO2Me > CF3.
BibTeX:
@article{Sauer1997,
author = {Sauer, Jurgen and Breu, Josef and Holland, Uwe and Herges, Rainer and Neumann, Helfried and Kammermeier, Stefan.},
title = {Diels-Alder reactions of tetradehydrodianthracene with electron-deficient dienes.},
journal = {Liebigs Ann./Recl.},
year = {1997},
pages = {1473-1479},
doi = {http://doi.org/10.1002/jlac.199719970726}
}
Photoresponsive carboxylic acids.
R. Herges and W. Reif, Liebigs Ann. 1996, 761-768.
Abstract:
A norbornadiene tetracarboxylic acid was prepd. the pKa of which can be changed by irradn. forming the quadricyclane deriv. or by catalytic reisomerization to the norbornadiene. The pKa difference of both isomers in the 2nd and 4th dissocn. step is 0.59 and 0.68 units. Photochem. isomerization proceeds without decompn. at pH >= 9.0. Reisomerization of the quadricyclane to the norbornadiene with a Rh(I) complex is also a clean reaction, but rather slow with t1/2 = 5 d at room temp. The pH change of an aq. soln. during isomerization is due to the formation or cleavage of intramol. H bonds between the adjacent carboxyl groups and accumulation or dispersion of neg. charge in the quadricyclane and norbornadiene, resp.
BibTeX:
@article{Herges1996,
author = {Herges, Rainer and Reif, Wolfgang.},
title = {Photoresponsive carboxylic acids.},
journal = {Liebigs Ann.},
year = {1996},
pages = {761-768},
doi = {http://doi.org/10.1002/jlac.15719960520}
}
Synthesis and Fragmentation of 2,2-Diazido-1,3,2-dioxasila-5-cycloheptenes. The Chemical Vapor Deposition of SiO2.
R. Herges and F. Starck, J. Am. Chem. Soc. 1996, 118, 12752-12757.
Abstract:
Ab initio (MP2/6-31G*) and d. functional theory (DFT, B3LYP/6-31G*) calcns. were performed to check the feasibility for the fragmentation of 1,3,2-dioxasila-5-cycloheptene-2-diyl to form SiO2. According to theor. results, the reaction is not synchronous but concerted and endergonic and requires an energy of activation of .apprx.50-60 kcal mol-1. Semiempirical calcns. (PM3) indicate that the process should be favored as a CVD process at the growing surface of quartz. For the exptl. realization of the fragmentation reaction the corresponding diazido silanes were chosen as silylene precursors. Two different strategies for the synthesis of 4,4',7,7'-tetramethyl-2,2-diazido-1,3,2-dioxasila-5-cycloheptene are presented. Unlike the 4,7-dimethyl- and the unsubstituted system, the tetra-Me deriv. is stable toward polymn. It decomps. under flash-vacuum pyrolysis conditions at 650 Deg and can be used for the CVD of amorphous quartz.
BibTeX:
@article{Herges1996a,
author = {Herges, Rainer and Starck, Felix.},
title = {Synthesis and Fragmentation of 2,2-Diazido-1,3,2-dioxasila-5-cycloheptenes. The Chemical Vapor Deposition of SiO2.},
journal = {J. Am. Chem. Soc.},
year = {1996},
volume = {118},
pages = {12752-12757},
doi = {http://doi.org/10.1021/ja9615886}
}
Photochemically induced metathesis reactions of tetradehydrodianthracene: synthesis and structure of bianthraquinodimethanes.
S. Kammermeier and R. Herges, Angew. Chem., Int. Ed. Engl. 1996, 35, 417-19.
Abstract:
Photochem. [2 + 2] cycloaddns. of tetradehydrodianthracene with a no. of alkenes and cycloalkenes were carried out and the structures of the product bianthraquinodimethanes detd. by 1H NMR and X-ray anal.
BibTeX:
@article{Kammermeier1996,
author = {Kammermeier, Stefan and Herges, Rainer.},
title = {Photochemically induced metathesis reactions of tetradehydrodianthracene: synthesis and structure of bianthraquinodimethanes.},
journal = {Angew. Chem., Int. Ed. Engl.},
year = {1996},
volume = {35},
pages = {417-19},
doi = {http://doi.org/10.1002/anie.199604171}
}
Diels-Alder reactions of tetradehydrodianthracene with electron-rich dienes.
S. Kammermeier, H. Neumann, F. Hampel and R. Herges, Liebigs Ann. 1996, 1795-1800.
Abstract:
Tetradehydrodianthracene (I) reacts with electron-rich dienes such as butadiene, cyclopentadiene, and 1,2-quinodimethane under ambient conditions. Only 1:1 products were obsd. even with a large excess of the diene and under drastic conditions, even though 2 strained and highly pyramidalized double bonds are available. The enhanced reactivity of I compared with its mono Diels-Alder adducts is mainly due to the through-bond and through-space interaction of the 2 olefinic double bonds. During the cycloaddn. one of the olefinic bonds in I is converted into an extremely long C-C single bond (>1.65 .ANG.). Attempts to cleave the strained s-bond in the cycloadduct from butadiene thermodynamically to form a diradical afforded a ring-opened isomer formed via a formal intramol. homo 1,3-sigmatropic shift.
BibTeX:
@article{Kammermeier1996a,
author = {Kammermeier, Stefan and Neumann, Helfried and Hampel, Frank and Herges, Rainer.},
title = {Diels-Alder reactions of tetradehydrodianthracene with electron-rich dienes.},
journal = {Liebigs Ann.},
year = {1996},
pages = {1795-1800},
doi = {http://doi.org/10.1002/jlac.199619961113}
}
Ring-expanding metathesis of tetradehydroanthracene - synthesis and structure of a tubelike, fully conjugated hydrocarbon.
S. Kammermeier, P.G. Jones and R. Herges, Angew. Chem., Int. Ed. Engl. 1996, 35, 2669-2671.
Abstract:
A tube-like hydrocarbon was prepd. via ring expansion metathesis and dimerization of 9,9',10,10'-tetradehydrodianthracene.
BibTeX:
@article{Kammermeier1996b,
author = {Kammermeier, Stefan and Jones, Peter G. and Herges, Rainer.},
title = {Ring-expanding metathesis of tetradehydroanthracene - synthesis and structure of a tubelike, fully conjugated hydrocarbon.},
journal = {Angew. Chem., Int. Ed. Engl.},
year = {1996},
volume = {35},
pages = {2669-2671},
doi = {http://doi.org/10.1002/anie.199626691}
}
(Iso)Pagodane Radical Cations in Liquid Hydrocarbons: "Time-Resolved Fluorescence-Detected Magnetic Resonance" Study of Valence Isomeric Radical Cations.
A.D. Trifunac, D.W. Werst, R. Herges, H. Neumann, H. Prinzbach and M. Etzkorn, J. Am. Chem. Soc. 1996, 118, 9444-9445.
Abstract:
The thermodn. unstable tight cyclobutanoid radical cation I is obsd. in hexane by FDMR and the activation barrier for its valence isomerization to the thermodn. more stable extended cyclobutanoid radical cation II is detd. Similar results for the ionization of isopagodane in hexane and the generation, observation and valence isomerization of isopagodane radical cations were less clear. The obsd. ESR and PMP2 calcns. of I, II and related isopagodane radical cations and valence isomerization hypersurfaces are discussed.
BibTeX:
@article{Trifunac1996,
author = {Trifunac, Alexander D. and Werst, David W. and Herges, Rainer and Neumann, Helfried and Prinzbach, Horst and Etzkorn, Markus.},
title = {(Iso)Pagodane Radical Cations in Liquid Hydrocarbons: "Time-Resolved Fluorescence-Detected Magnetic Resonance" Study of Valence Isomeric Radical Cations.},
journal = {J. Am. Chem. Soc.},
year = {1996},
volume = {118},
pages = {9444-9445},
doi = {http://doi.org/10.1021/ja961035v}
}
Simulation of infrared spectra using artificial neural networks based on semiempirical and empirical data.
U.M. Weigel and R. Herges, Anal. Chim. Acta 1996, 331, 63-74.
Abstract:
Two different methods using artificial neural networks of the backpropagation type were applied to simulate IR spectra of org. CHO compds. Their performance is compared. The 1st method uses harmonic frequencies and intensities of a semiempirical (AM1) calcn. and the 2nd one, a list of substructures of the corresponding compd. as input for the neural net. Both the networks are trained to derive the exptl. spectra from the corresponding quantum chem. or structural input information. A set of 840 CHO compds. from the Specinfo database was used for training. Extensive studies to evaluate the quality of the simulated spectra were made. Both the methods are comparable in their performance. The quality of simulation is reasonable within the range of 4000-1300 cm-1, however, the methods fail to predict the fingerprint region (1300-400 cm-1).
BibTeX:
@article{Weigel1996,
author = {Weigel, U. M. and Herges, R..},
title = {Simulation of infrared spectra using artificial neural networks based on semiempirical and empirical data.},
journal = {Anal. Chim. Acta},
year = {1996},
volume = {331},
pages = {63-74},
doi = {http://doi.org/10.1016/0003-2670(96)00203-6}
}
Nature of the Interaction of Olefin-Bromine Complexes. Inference from (E)-2,2,5,5-Tetramethyl-3,4-diphenylhex-3-ene, the First Example of an Olefin Whose Reaction with Bromine Stops at the Stage of pi Complex Formation.
G. Bellucci, C. Chiappe, R. Bianchini, D. Lenoir and R. Herges, J. Am. Chem. Soc. 1995, 117, 12001-2.
Abstract:
The title sterically congested olefin forms with Br2 in 1,2-dichloroethane a 1:1 pi complex at the olefin double bond, with Kf = 1.2(0.1) M-1 at 25 Deg, Delta H = -3.25(0.13) kcal mol-1 and Delta S = -10.6(0.5) eu, which does not further evolve to a bromonium salt. The 1H and 13C NMR spectra of this complex in dichloromethane-d2 are identical to those of the free olefin, showing that complex formation is not accompanied by a significant transfer of neg. charge from the double bond to Br2. This is in agreement with ab initio calcns. on the parent model system ethylene + Br2.
BibTeX:
@article{Bellucci1995,
author = {Bellucci, Giuseppe and Chiappe, Cinzia and Bianchini, Roberto and Lenoir, Dieter and Herges, Rainer.},
title = {Nature of the Interaction of Olefin-Bromine Complexes. Inference from (E)-2,2,5,5-Tetramethyl-3,4-diphenylhex-3-ene, the First Example of an Olefin Whose Reaction with Bromine Stops at the Stage of pi Complex Formation.},
journal = {J. Am. Chem. Soc.},
year = {1995},
volume = {117},
pages = {12001-2},
doi = {http://doi.org/10.1021/ja00153a025}
}
4c/3e radical cations with cage-directed configurations.
G. Gescheidt, R. Herges, H. Neumann, J. Heinze, M. Wollenweber, M. Etzkorn and H. Prinzbach, Angew. Chem., Int. Ed. Engl. 1995, 34, 1016-19.
Abstract:
ESR and ENDOR spectra of the radical cations generated from I and II were given. The designation of the short-lived radical radical cation derived from I as as tight and that of the longer lived ion derived from II as extended is corroborated by ab initio and INDO calcns. The geometries were optimized at the UHF/3-21G level and confirmed as min. by harmonic frequency anal. ESR coupling const. calcd. by the INDO method are based on ab initio geometries. According to these calcns. both [2.2.1.1]pagodanes exhibit two min. corresponding to the tight and extended ions; for I the tight, for II the extended structure is the more stable isomer. The sym. (concerted) transition tight -> extended is forbidden since both species in each system have different symmetries.
BibTeX:
@article{Gescheidt1995,
author = {Gescheidt, Georg and Herges, Rainer and Neumann, Helfried and Heinze, Juergen and Wollenweber, Markus and Etzkorn, Markus and Prinzbach, Horst.},
title = {4c/3e radical cations with cage-directed configurations.},
journal = {Angew. Chem., Int. Ed. Engl.},
year = {1995},
volume = {34},
pages = {1016-19},
doi = {http://doi.org/10.1002/anie.199510161}
}
Prediction of Chromatographic Retention Values (RM) and Partition Coefficients (log Poct) Using a Combination of Semiempirical Self-Consistent Reaction Field Calculations and Neural Networks.
J. Grunenberg and R. Herges, J. Chem. Inf. Comput. Sci. 1995, 35, 905-11.
Abstract:
A combination of semiempirical solvent effect calcns. and artificial neural networks was used to predict the (reversed phase) retention values (RM) of steroids and the partition coeffs. (log Poct) of a diverse set of org. compds. Eleven selected phys. parameters from AM1 self-consistent reaction field calcns. were used as input for neural networks of the back-propagation type. The performance (std. error 0.08 RM units) in predicting retention values of a set of steroids is close to exptl. accuracy (0.03 RM units). The partition coeffs. of a heterogeneous set of org. compds. are predicted with a std. error of 0.29 log Poct units. Systematic leave-n-out expts. revealed that the solvation energy obtained by simple solvent calcns. (spherical model) is the most important parameter in the authors' 11 parameter set and considerably improves the performance in predicting hydrophobicity at little addnl. computational cost.
BibTeX:
@article{Grunenberg1995,
author = {Grunenberg, J. and Herges, R..},
title = {Prediction of Chromatographic Retention Values (RM) and Partition Coefficients (log Poct) Using a Combination of Semiempirical Self-Consistent Reaction Field Calculations and Neural Networks.},
journal = {J. Chem. Inf. Comput. Sci.},
year = {1995},
volume = {35},
pages = {905-11},
doi = {http://doi.org/10.1021/ci00027a018}
}
Discovering reaction principles using reaction data bases and quantum chemistry.
R. Herges, Book of Abstracts, 210th ACS National Meeting, Chicago, IL, August 20-24 1995, CINF-047.
Abstract:
Reaction data bases contain a wealth of hidden information in addn. to the routinely used search and retrieval capabilities. General rules and reaction principles can be derived by a systematic anal. of the data. We used a hierarchical classification algorithm to scrutinize 80 000 reactions within reaction data bases. Most of the examples fall into well known reaction categories. However, within the remaining data set, we discovered a group of reactions that exhibit obvious relationships which have not been recognized so far. We were able to explain these descriptive relationships on a quantum chem. basis. The theor. formalism can be reduced to simple rules that predict the stereochem. of these reactions similar to the Woodward-Hoffmann rules. Moreover, a simple algorithm was derived to predict new reactions of this category. Finally, we were able to verify two of these reactions in the lab.
BibTeX:
@conference{Herges1995,
author = {Herges, R..},
title = {Discovering reaction principles using reaction data bases and quantum chemistry.},
journal = {Book of Abstracts, 210th ACS National Meeting, Chicago, IL, August 20-24},
year = {1995},
pages = {CINF-047}
}
New findings in the electrophilic addition of halogens to olefins.
R. Herges, Angew. Chem., Int. Ed. Engl. 1995, 34, 51-3.
Abstract:
A review with 33 refs.
BibTeX:
@article{Herges1995a,
author = {Herges, Rainer.},
title = {New findings in the electrophilic addition of halogens to olefins.},
journal = {Angew. Chem., Int. Ed. Engl.},
year = {1995},
volume = {34},
pages = {51-3},
doi = {http://doi.org/10.1002/anie.199500511}
}
Electrophilic additions to tetradehydrodianthracene.
R. Herges and H. Neumann, Liebigs Ann. 1995, 1283-9.
Abstract:
5,12[1',2']:6,11[1'',2'']-Dibenzenodibenzo[a,e]cyclooctene (tetradehydrodianthracene, TDDA) reacts with halogens to give transannular (anti) and ring-opened (syn) products. The product ratio shows a remarkable solvent dependence. Solvents of medium polarity favor anti addn., whereas syn addn. is obsd. both with increasing and decreasing polarity. For instance, chlorine in toluene adds 100% syn, in dichloroethane 56% anti, and in trifluorethanol again 100% syn. It is concluded that, depending on solvent polarity, three difference mechanisms for electrophilic addn. are operative.
BibTeX:
@article{Herges1995b,
author = {Herges, Rainer and Neumann, Helfried.},
title = {Electrophilic additions to tetradehydrodianthracene.},
journal = {Liebigs Ann.},
year = {1995},
pages = {1283-9},
doi = {http://doi.org/10.1002/jlac.1995199507170}
}
4c/3e Radical Cations Sustained in Hydrocarbon Cages. The [1.1.1.1](Iso)pagodane Cases.
H. Prinzbach, M. Wollenweber, R. Herges, H. Neumann, G. Gescheidt and R. Schmidlin, J. Am. Chem. Soc. 1995, 117, 1439-40.
Abstract:
It is demonstrated by ESR (ENDOR) spectroscopy and ab initio calcns. that the radical cations derived from [1.1.1.1]pagodane (and its valence isomeric diene 2) and from [1.1.1.1]isopagodane 3, peralkylated caged cyclobutanes, are delocalized 4c/3e species yet are of highly different stability (persistence) and of different configuration (2.bul.+, extended; 3.bul.+, tight, cyclobutanoid). 2.bul.+ And 3.bul.+ represent two points of an exptl. reaction coordinate for ethylene/ethylene.bul.+ cycloaddn. (D2h) which will be supplemented with radical cations generated from related geometrically tuned cage structures.
BibTeX:
@article{Prinzbach1995,
author = {Prinzbach, Horst and Wollenweber, Markus and Herges, Rainer and Neumann, Helfried and Gescheidt, Georg and Schmidlin, Reto.},
title = {4c/3e Radical Cations Sustained in Hydrocarbon Cages. The [1.1.1.1](Iso)pagodane Cases.},
journal = {J. Am. Chem. Soc.},
year = {1995},
volume = {117},
pages = {1439-40},
doi = {http://doi.org/10.1021/ja00109a033}
}
Cyclic electron delocalization in hydrocarbon cages (pagodanes, isopagodanes, (bisseco-/seco-)(dodecahedradienes).
H. Prinzbach, G. Gescheidt, H.D. Martin, R. Herges, J. Heinze, G.K. Surya Prakash and G.A. Olah, Pure Appl. Chem. 1995, 67, 673-82.
Abstract:
A symposium. In the polycyclic, rigid [1.1.1.1]/[2.2.1.1] (iso)pagodanes and in the related (bisseco/seco)dodecahedradienes the geometrical and energetical situation for the 4c/3e radical cations and 4c/2e dications produced by loss of one or two electrons from the central cyclobutane/homodiene cores is gradually modified. By spectroscopic (UV, PE, ESR, NMR), cyclovoltammetric, and theor. investigations, the structural prerequisites and the degree of homoconjugational (through-cage) electron delocalization (s-homoaromaticity) are explored.
BibTeX:
@article{Prinzbach1995a,
author = {Prinzbach, H. and Gescheidt, G. and Martin, H. D. and Herges, R. and Heinze, J. and Surya Prakash, G. K. and Olah, G. A.},
title = {Cyclic electron delocalization in hydrocarbon cages (pagodanes, isopagodanes, (bisseco-/seco-)(dodecahedradienes).},
journal = {Pure Appl. Chem.},
year = {1995},
volume = {67},
pages = {673-82},
doi = {http://doi.org/10.1351/pac199567050673}
}
Coarctate transition states: the discovery of a reaction principle.
R. Herges, J. Chem. Inf. Comput. Sci. 1994, 34, 91-102.
Abstract:
A computer-aided classification of >80,000 reactions from reaction databases and manual classification of several thousand reactions from the literature suggested that there are three major topols. of electron redistribution in single-step reactions. The linear (e.g., addn., substitution, elimination) and the cyclic (pericyclic) topol. correspond to the most common and fundamental ways of mechanistic thinking in org. chem. Among the remaining reactions, there is a third class sharing a common topol. of electron redistribution that the authors call coarctate. The authors proved that the obvious relationships of these reactions are based on a common phys. principle. They seem to form a third, small but important category of org. reactions that hitherto never have been described in a coherent context.
BibTeX:
@article{Herges1994,
author = {Herges, R..},
title = {Coarctate transition states: the discovery of a reaction principle.},
journal = {J. Chem. Inf. Comput. Sci.},
year = {1994},
volume = {34},
pages = {91-102},
doi = {http://doi.org/10.1021/ci00017a011}
}
Ordering principle of complex reactions and theory of contracted transition states.
R. Herges, Angew. Chem. 1994, 106, 261-83 (See also Angew. Chem., Int. Ed. Engl., 1994, 33(3), 255-76).
Abstract:
A review with over 212 refs.
BibTeX:
@article{Herges1994a,
author = {Herges, Rainer.},
title = {Ordering principle of complex reactions and theory of contracted transition states.},
journal = {Angew. Chem.},
year = {1994},
volume = {106},
pages = {261-83 (See also Angew. Chem., Int. Ed. Engl., 1994, 33(3), 255-76)},
doi = {http://doi.org/10.1002/ange.19941060304}
}
Synthesis of methyl 6,6-dimethylfulvene-2-carboxylate and dimethyl 6,6-dimethylfulvene-2,3-dicarboxylate as well as their conversion to 2,3,5,6-substituent norbornadienes.
R. Herges and W. Reif, Chem. Ber. 1994, 127, 1143-5.
Abstract:
Fulvenes I and II were synthesized by Diels-Alder reaction of 6,6-dimethylfulvene with Me prop-2-ynoate and di-Me but-2-ynedioate, catalytic redn. of the unsubstituted norbornadiene double bond, and a subsequent retro Diels-Alder reaction under flash vacuum pyrolysis conditions. I and II are used as the diene component in synthesizing 2,5-, 2,3,5-, and 2,3,5,6-substituted III by Diels-Alder reaction with electron-deficient alkynes IV and V.
BibTeX:
@article{Herges1994b,
author = {Herges, Rainer and Reif, Wolfgang.},
title = {Synthesis of methyl 6,6-dimethylfulvene-2-carboxylate and dimethyl 6,6-dimethylfulvene-2,3-dicarboxylate as well as their conversion to 2,3,5,6-substituent norbornadienes.},
journal = {Chem. Ber.},
year = {1994},
volume = {127},
pages = {1143-5},
doi = {http://doi.org/10.1002/cber.19941270627}
}
Propargylene.
R. Herges and A. Mebel, J. Am. Chem. Soc. 1994, 116, 8229-37.
Abstract:
A theor. investigation has been performed on triplet and singlet propargylene (C3H2, ethynylcarbene) using various levels of ab initio theory [MP2, MP4, QCISD, QCISD(T), and multireference CI]. According to the results, and in contradiction to earlier calcns., neither the singlet nor the triplet propargylene is a carbene. Vibrational frequencies of the 1,3-diradicaloid C2 structure of triplet propargylene are in much better agreement with expt. than those of the Cs carbene structure. The hitherto assumed transition state (C2v) of the singlet propargylene automerization is a min., and the singlet (like the triplet) carbene structure (Cs) is not a stationary point on the energy hypersurface at the QCISD(T)/6-31G* level. The singlet-triplet gap is much larger than previously assumed, and the rotational lines of triplet propargylene are shifted to lower frequencies compared to earlier calcns.
BibTeX:
@article{Herges1994c,
author = {Herges, Rainer and Mebel, Alexander.},
title = {Propargylene.},
journal = {J. Am. Chem. Soc.},
year = {1994},
volume = {116},
pages = {8229-37},
doi = {http://doi.org/10.1021/ja00097a032}
}
Transannular addition of methyllithium to 5,12:6,11-di[1,2]benzenodibenzo[a,e]cyclooctene and its 5,6-epoxy derivative.
R. Herges, H. Neumann and F. Hampel, Angew. Chem. 1994, 106, 1024-6 (See also Angew. Chem. Int. Ed. Engl., 1994, 33(9), 993-5).
Abstract:
Transannular addn. reactions of the title compds., i.e., epoxytetradehydrodianthracene and tetradehydrodianthracene (I) were studied.
BibTeX:
@article{Herges1994d,
author = {Herges, Rainer and Neumann, Helfried and Hampel, Frank.},
title = {Transannular addition of methyllithium to 5,12:6,11-di[1,2]benzenodibenzo[a,e]cyclooctene and its 5,6-epoxy derivative.},
journal = {Angew. Chem.},
year = {1994},
volume = {106},
pages = {1024-6 (See also Angew. Chem. Int. Ed. Engl., 1994, 33(9), 993-5)},
doi = {http://doi.org/10.1002/ange.19941060912}
}
Magnetic properties of aromatic transition states: the Diels-Alder reaction.
R. Herges, H. Jiao and P. v.R. Schleyer, Angew. Chem. 1994, 106, 1441-4.
Abstract:
Magnetic properties are shown to be a useful criterion for pericyclic transition states. The Diels-Alder reactions of ethene with 1,3-butadiene and 1,3-cyclopentadiene are examd. by quantum chem. methods.
BibTeX:
@article{Herges1994e,
author = {Herges, Rainer and Jiao, Haijun and Schleyer, Paul von Rague.},
title = {Magnetic properties of aromatic transition states: the Diels-Alder reaction.},
journal = {Angew. Chem.},
year = {1994},
volume = {106},
pages = {1441-4},
doi = {http://doi.org/10.1002/ange.19941061320}
}
Computer-assisted solution of chemical problems: a new discipline in chemistry.
I. Ugi, J. Bauer, K. Bley, A. Dengler, A. Dietz, E. Fontain, B. Gruber, R. Herges, M. Knauer and et al., Angew. Chem. 1993, 105, 210-39 (See also Angew. Chem., Int. Ed. Engl., 1993, 32(2), 201-27).
Abstract:
A review with 226 refs.
BibTeX:
@article{Ugi1993,
author = {Ugi, Ivar and Bauer, Johannes and Bley, Klemens and Dengler, Alf and Dietz, Andreas and Fontain, Eric and Gruber, Bernhard and Herges, Rainer and Knauer, Michael and et al.},
title = {Computer-assisted solution of chemical problems: a new discipline in chemistry.},
journal = {Angew. Chem.},
year = {1993},
volume = {105},
pages = {210-39 (See also Angew. Chem., Int. Ed. Engl., 1993, 32(2), 201-27)},
doi = {http://doi.org/10.1002/ange.19931050207}
}
Reaction planning: computer-aided discovery of a novel elimination reaction.
R. Herges and C. Hoock, Science (Washington, D. C., 1883-) 1992, 255, 711-13.
Abstract:
Algorithms based on graph theory and implemented in a computer program have been used to search for unprecedented reactions. This approach is illustrated by a systematic and exhaustive screening of pericyclic reactions in order to find new reactions useful in the synthesis of conjugated dienes. Two reactions were found. They were optimized by structural variation with the aid of quantum-chem. calcns. and were then exptl. verified. E.g. the tosylhydrazone of dithiapine I was heated to give butadiene and carbon disulfide product.
BibTeX:
@article{Herges1992,
author = {Herges, Rainer and Hoock, Christoph.},
title = {Reaction planning: computer-aided discovery of a novel elimination reaction.},
journal = {Science (Washington, D. C., 1883-)},
year = {1992},
volume = {255},
pages = {711-13},
doi = {http://doi.org/10.1126/science.255.5045.711}
}
Butatrienes via desulfurization of cyclic trithiocarbonates.
R. Herges and C. Hoock, Angew. Chem. 1992, 104, 1652-4 (See also Angew. Chem., Int. Ed. Engl., 1992, 31(12), 1611-13).
Abstract:
RCH:C:C:CHR (R = H, Me, CHMe2) were prepd. as 1:1 E,Z mixts. by treating 4-MeC6H4SO3CHRC==CCHRO3SC6H4Me-4 with K2CS3 and desulfurizing the dithiolanethiones I with Raney Ni poisoned with PhCOMe or Ph2CO.
BibTeX:
@article{Herges1992a,
author = {Herges, Rainer and Hoock, Christoph.},
title = {Butatrienes via desulfurization of cyclic trithiocarbonates.},
journal = {Angew. Chem.},
year = {1992},
volume = {104},
pages = {1652-4 (See also Angew. Chem., Int. Ed. Engl., 1992, 31(12), 1611-13)},
doi = {http://doi.org/10.1002/ange.19921041223}
}
Automatic interpretation of infrared spectra: recognition of aromatic substitution patterns using neural networks.
U.M. Weigel and R. Herges, J. Chem. Inf. Comput. Sci. 1992, 32, 723-31.
Abstract:
Several neural networks of back-propagation type were trained to reorganize and to identify the substitution patterns of differently substituted arom. compds. by pattern anal. of their IR spectra. The effect of network architecture and input design on the predictive performance of the neural net was examd. The neural nets were trained with a set of IR spectra of mono-, di (1,2; 1,3; 1,4)-, tri (1,2,3; 1,3,5; 1,2,4)- and tetrasubstituted (1,2,3,4; 1,2,3,5; 1,2,3,5)- arom. compds. After training they were able to interpret spectra of arom. compds. not included in the training set. The accuracy in recognizing the proper substitution pattern ranges from fair to excellent, depending on the model and the training set.
BibTeX:
@article{Weigel1992,
author = {Weigel, U. M. and Herges, R..},
title = {Automatic interpretation of infrared spectra: recognition of aromatic substitution patterns using neural networks.},
journal = {J. Chem. Inf. Comput. Sci.},
year = {1992},
volume = {32},
pages = {723-31},
doi = {http://doi.org/10.1021/ci00010a021}
}
Tetramethylene dications (CH2)42+: are the norbornadiene dication, the pagodane dication, and related systems aromatic?
R. Herges, P. v.R. Schleyer, M. Schindler and W.D. Fessner, J. Am. Chem. Soc. 1991, 113, 3649-56.
Abstract:
The (CH2)42+ potential energy hypersurface has been investigated by semiempirical and ab initio calcns. The global min. is an acyclic structure of Ci symmetry. Harmonic vibrational anal. of the rectangular cyclobutane dication (D2h), which serves as a model for s-arom. pagodane and norbornadiene dications, indicates three imaginary frequencies. Nonetheless, strong evidence that the pagodane dication has a nonclassical, arom. structure of D2h symmetry is presented. A rapid equil. of two classical C2v structures and a diradical D2h species in which both are consistent with the exptl. NMR spectroscopic data can be excluded on the basis of the theor. investigations. The norbornadiene dication is also predicted to be stabilized by aromaticity, whereas structures with larger distances between the two formal ethylene radical cations are predicted to exhibit increasing diradicaloid character.
BibTeX:
@article{Herges1991,
author = {Herges, Rainer and Schleyer, Paul v. R. and Schindler, Michael and Fessner, Wolf Dieter.},
title = {Tetramethylene dications (CH2)42+: are the norbornadiene dication, the pagodane dication, and related systems aromatic?},
journal = {J. Am. Chem. Soc.},
year = {1991},
volume = {113},
pages = {3649-56},
doi = {http://doi.org/10.1021/ja00010a003}
}
A novel butatriene synthesis.
R. Herges and C. Hoock, Synthesis 1991, 1151-2.
Abstract:
Reaction of potassium trithiocarbonate with 1,4-dichloro-, 1,4-bis(tosyloxy)- or 1,4-dibromo-2-butyne in CH2Cl2 contg. a catalytic amt. of 18-crown-6 afforded 75% 4-vinylidene-1,3-dithiolane-2-thione (I). The trithiocarbonate I is desulfurized with 1,2-dimethyl-2-phenyl-1,3,2-diazaphospholidine to give 85-90% butatriene under very mild conditions.
BibTeX:
@article{Herges1991a,
author = {Herges, Rainer and Hoock, Christoph.},
title = {A novel butatriene synthesis.},
journal = {Synthesis},
year = {1991},
pages = {1151-2},
doi = {http://doi.org/10.1055/s-1991-28408}
}
Reaction planning: prediction of new organic reactions.
R. Herges, J. Chem. Inf. Comput. Sci. 1990, 30, 377-83.
Abstract:
A new algorithm for the generation of the complete set of nonisomorphic spanning subgraphs of a given graph or pseudograph is presented. With this procedure unprecedented org. reactions can be predicted. A predicted new carbene reaction, which has been subsequently verified in the lab., serves as an example.
BibTeX:
@article{Herges1990,
author = {Herges, Rainer.},
title = {Reaction planning: prediction of new organic reactions.},
journal = {J. Chem. Inf. Comput. Sci.},
year = {1990},
volume = {30},
pages = {377-83},
doi = {http://doi.org/10.1021/ci00068a006}
}
The reaction of tropone with a homopyrrole as the result of a computer-assisted search of precedent-setting chemical reactions.
D. Forstmeyer, J. Bauer, E. Fontain, R. Herges, R. Herrmann and I. Ugi, Angew. Chem. 1988, 100, 1618-19.
Abstract:
The reaction of homopyrrole I with tropone gave 92% cycloadduct II.
BibTeX:
@article{Forstmeyer1988,
author = {Forstmeyer, Dietmar and Bauer, Johannes and Fontain, Eric and Herges, Rainer and Herrmann, Rudolf and Ugi, Ivar.},
title = {The reaction of tropone with a homopyrrole as the result of a computer-assisted search of precedent-setting chemical reactions.},
journal = {Angew. Chem.},
year = {1988},
volume = {100},
pages = {1618-19},
doi = {http://doi.org/10.1002/ange.19881001137}
}
Reaction planning: computer-aided reaction design.
R. Herges, Tetrahedron Comput. Methodol. 1988, 1, 15-26.
Abstract:
A new concept for the search for unprecedented chem. reactions is presented. With the aid of the expert system IGOR the complete set of pericyclic reaction schemes (up to 8 reacting atoms) has been generated. The result looks like a periodic table of conceivable reactions. Some rows contain unknown reactions. They can be predicted. In this article the design of two of these new reactions, aimed at the syntheses of given classes of compds., is described. They both have been verified exptl.
BibTeX:
@article{Herges1988,
author = {Herges, Rainer.},
title = {Reaction planning: computer-aided reaction design.},
journal = {Tetrahedron Comput. Methodol.},
year = {1988},
volume = {1},
pages = {15-26},
doi = {http://doi.org/10.1016/0898-5529(88)90005-X}
}
Stable carbocations. 273. [1.1.1.1]- and [2.2.1.1]Pagodane dications: frozen two-electron Woodward-Hoffmann transition-state models.
G.K.S. Prakash, V.V. Krishnamurthy, R. Herges, R. Bau, H. Yuan, G.A. Olah, W.D. Fessner and H. Prinzbach, J. Am. Chem. Soc. 1988, 110, 7764-72.
Abstract:
[1.1.1.1]- And [2.2.1.1]pagodanes [I, N = 1 (II, 2 (III), resp.] were oxidized in SbF5/SO2ClF at -78 Deg via two-electron removal from the central cyclobutane ring to give the dications IV [(N = 1 V, 2 (VI)]. Dication V is also formed selectively by two-electron oxidn. of a diene valence isomer VII and by ionization of dibromide VIII. Dication V is stable at ambient temp. for hours, while the bishomologous VI rearranges to a bisallylic dication, even at -78 Deg. The tight structural prerequisites for the stability of such dications are further substantiated by the observation that from several related cyclobutanoid cage compds., e.g., cubane, homocubane IX, and X, when exposed to the same oxidative conditions, no distinct dications could be obsd. On the basis of 1H and 13C NMR chem. shift criteria, supported by pertinent SCF-MO calcns., the dications obtained are considered as novel four-center/two-electron delocalized bishomoarom. species, which resemble two-electron Woodward-Hoffmann transition states and owe their unprecedented character to their specific rigid framework. The reliability of the calcns. in handling cage mols. of this type and size is evaluated in a comparison with structural data provided by single crystal x-ray structure detns. for II and III and a dimethoxy analog to VIII.
BibTeX:
@article{Prakash1988,
author = {Prakash, G. K. Surya and Krishnamurthy, V. V. and Herges, Rainer and Bau, Robert and Yuan, Hanna and Olah, George A. and Fessner, Wolf Dieter and Prinzbach, Horst.},
title = {Stable carbocations. 273. [1.1.1.1]- and [2.2.1.1]Pagodane dications: frozen two-electron Woodward-Hoffmann transition-state models.},
journal = {J. Am. Chem. Soc.},
year = {1988},
volume = {110},
pages = {7764-72},
doi = {http://doi.org/10.1021/ja00231a029}
}
Cycloadditions with homodienes.
R. Herges and I. Ugi, Chem. Ber. 1986, 119, 829-36.
Abstract:
In CH2Cl2 or CHCl3, homofuran (I; R = H) reacted with TCNE via [(s2 + pi2) + pi2] cycloaddn. to give adduct II, whereas II was a minor product in MeCN and the [pi2 + pi2] adduct (III) was the main product. In MeOH the intermediate in III formation was trapped, but the II yield was not affected appreciably. In MeCN the half-life of the 1,4-dipolar intermediate of the [2 + 2] addn. was almost 3 h. Rate consts. and activation parameters were detd., and the reaction of I (R = Me) with TCNE was also described.
BibTeX:
@article{Herges1986,
author = {Herges, Rainer and Ugi, Ivar.},
title = {Cycloadditions with homodienes.},
journal = {Chem. Ber.},
year = {1986},
volume = {119},
pages = {829-36},
doi = {http://doi.org/10.1002/cber.19861190306}
}
Improved preparation of 2-oxabicyclo[3.1.0]hex-3-ene (homofuran) and 2-thiabicyclo[3.1.0]hex-3-ene (homothiophene).
R. Herges and I. Ugi, Synthesis 1986, 1059.
Abstract:
Addn. of carbene to furan or thiophene in the presence of CuCl with excess furan or thiophene as solvent gave 65% homofuran (I, X = O) and 6% homothiophene (I, X = S), resp.
BibTeX:
@article{Herges1986a,
author = {Herges, Rainer and Ugi, Ivar.},
title = {Improved preparation of 2-oxabicyclo[3.1.0]hex-3-ene (homofuran) and 2-thiabicyclo[3.1.0]hex-3-ene (homothiophene).},
journal = {Synthesis},
year = {1986},
pages = {1059},
doi = {http://doi.org/10.1055/s-1986-31875}
}
Onium ions. 34. The methoxydiazonium ion: preparation, proton, carbon-13, and nitrogen-15 NMR and IR structural studies, theoretical calculations, and reaction with aromatics. Attempted preparation and the intermediacy of the hydroxydiazonium ion.
G.A. Olah, R. Herges, K. Laali and G.A. Segal, J. Am. Chem. Soc. 1986, 108, 2054-7.
Abstract:
N2O is methylated with MeF-SbF5 in SO2F2 or with MeO+ -SOClF in FSO2Cl to give the stable ion MeON2+ (I), which was characterized by NMR (15N, 13C, 1H) and FT-IR spectroscopic studies. I stable at <-30 Deg, above which it decomps., regenerating N2O. I gives only methylation products with aroms. such as PhMe, and no methoxy derivs. are formed. Spectroscopic and chem. data indicate that the mesomeric form MeON:N+ is a significant contributor to the overall structure of I. Consideration of computed charge distribution (4-31 G with full geometry optimization and 4-31G*) also supports this conclusion. Independent generation of I was also studied by solvolysis of MeN(O):NO3SCF3 and diazotization of MeONH2 with NO+ BF4-. Prepn. of the elusive HON2+ ion (II) was attempted by protonating N2O in superacids, but no long-lived ion was obsd. Diazotization of HONH2 with NO+ BF4- gives N2O, indicative of the intermediacy of II.
BibTeX:
@article{Olah1986,
author = {Olah, George A. and Herges, Rainer and Laali, Khosrow and Segal, Gerald A.},
title = {Onium ions. 34. The methoxydiazonium ion: preparation, proton, carbon-13, and nitrogen-15 NMR and IR structural studies, theoretical calculations, and reaction with aromatics. Attempted preparation and the intermediacy of the hydroxydiazonium ion.},
journal = {J. Am. Chem. Soc.},
year = {1986},
volume = {108},
pages = {2054-7},
doi = {http://doi.org/10.1021/ja00268a054}
}
Stable carbocations. Part 267. Pagodane dication, a unique 2pi-aromatic cyclobutanoid system.
G.K. Prakash, V.V. Krishnamurthy, R. Herges, R. Bau, H. Yuan, G.A. Olah, W.D. Fessner and H. Prinzbach, J. Am. Chem. Soc. 1986, 108, 836-8.
Abstract:
The central strained planar cyclobutane ring of pagodane (I), an undecacyclic C20H20 polyquinane, was found to undergo facile two electron s-oxidn. in superacidic SbF5/SO2ClF or SbF5/FSO3H/SO2ClF solns. at -78 Deg to give a surprisingly stable dication (II). Evidence for the unique arom. 2pi cyclobutanoid character of II has been obtained by 13C and 1H NMR spectroscopic data as well as by methanol quenching studies and is supported by theor. considerations.
BibTeX:
@article{Prakash1986,
author = {Prakash, G. K. and Krishnamurthy, V. V. and Herges, Rainer and Bau, Robert and Yuan, Hanna and Olah, George A. and Fessner, Wolf Dieter and Prinzbach, Horst.},
title = {Stable carbocations. Part 267. Pagodane dication, a unique 2pi-aromatic cyclobutanoid system.},
journal = {J. Am. Chem. Soc.},
year = {1986},
volume = {108},
pages = {836-8},
doi = {http://doi.org/10.1021/ja00264a046}
}
New reagents and methods for the synthesis of peptides, beta -lactams and oligonucleotides.
I. Ugi, H. Aigner, G. Glahsl, R. Herges, G. Hering, R. Herrmann, G. Huebener, J. Goetz, P. Lemmen and et al., Nat. Prod. Chem., Proc. Int. Symp. Pak.-U.S. Binatl. Workshop, 1st 1986, 457-84.
Abstract:
A review with 75 refs.
BibTeX:
@conference{Ugi1986,
author = {Ugi, Ivar and Aigner, Helmut and Glahsl, Gudrun and Herges, Rainer and Hering, Gabriele and Herrmann, Rudolf and Huebener, Gerd and Goetz, Josef and Lemmen, Peter and et al.},
title = {New reagents and methods for the synthesis of peptides, beta -lactams and oligonucleotides.},
journal = {Nat. Prod. Chem., Proc. Int. Symp. Pak.-U.S. Binatl. Workshop, 1st},
year = {1986},
pages = {457-84}
}
IGOR and computer assisted innovation in chemistry.
J. Bauer, R. Herges, E. Fontain and I. Ugi, Chimia 1985, 39, 43-53.
Abstract:
A review with 45 refs. on IGOR (interactive generation of org. reactions), the first general-purpose, artificial intelligence-type computer program for generating graphic representations of unprecedented chem. The potential role of artificial intelligence methods in research is discussed.
BibTeX:
@article{Bauer1985,
author = {Bauer, Johannes and Herges, Rainer and Fontain, Eric and Ugi, Ivar.},
title = {IGOR and computer assisted innovation in chemistry.},
journal = {Chimia},
year = {1985},
volume = {39},
pages = {43-53}
}
Synthesis of seven-membered rings by [(s2 + pi2) + pi2] cycloaddition on homodienes.
R. Herges and I. Ugi, Angew. Chem. 1985, 97, 596-7.
Abstract:
Cycloaddn. of TCNE with homofuran (I; X = O) in CH2Cl2 gave adduct II with Delta H.thermod. = 54.0 kJ mol-1 and Delta S.thermod. = -105.4 J mol-1 K-1. The II yield decreased and that of adduct III increased with increasing solvent polarity; in MeCN the II-III ratio was 23:77. Activation parameters were detd. for II and III formation in MeCN. I (X = O) cycloaddn. with maleic anhydride gave exo- and endo-IV. Hydrolysis and iodolactonization of exo-IV gave V; hydrolysis of endo-IV gave diacid VI. Cycloaddn. of I (X = S) with TCNE was also examd.
BibTeX:
@article{Herges1985,
author = {Herges, Rainer and Ugi, Ivar.},
title = {Synthesis of seven-membered rings by [(s2 + pi2) + pi2] cycloaddition on homodienes.},
journal = {Angew. Chem.},
year = {1985},
volume = {97},
pages = {596-7},
doi = {http://doi.org/10.1002/ange.19850970727}
}
Onium ions. 32. Intermediacy of the parent diazonium ion (protonated dinitrogen, N2+H) in the diazotization of ammonia and its derivatives with nitrosonium tetrafluoroborate (15NO+BF4-) giving 15N14N+.
G.A. Olah, R. Herges, J.D. Felberg and G.K.S. Prakash, J. Am. Chem. Soc. 1985, 107, 5282-3.
Abstract:
Diazotization of NH3, (Me3Si)2NH, and isocyanic acid with 95% 15NO+BF4- salt gives 15N14N involving the intermediacy of diazonium ion, HN2+ (I). Attempts to observe I in a stop-flow NMR expt. were unsuccessful. I once formed is extremely unstable and spontaneously deprotonates into N2 in accordance with the known low proton affinity of N2.
BibTeX:
@article{Olah1985,
author = {Olah, George A. and Herges, Rainer and Felberg, Jeff D. and Prakash, G. K. Surya.},
title = {Onium ions. 32. Intermediacy of the parent diazonium ion (protonated dinitrogen, N2+H) in the diazotization of ammonia and its derivatives with nitrosonium tetrafluoroborate (15NO+BF4-) giving 15N14N+.},
journal = {J. Am. Chem. Soc.},
year = {1985},
volume = {107},
pages = {5282-3},
doi = {http://doi.org/10.1021/ja00304a047}
}
Cycloheptatriene/norcaradiene. Valence isomerization and conformational effects.
H. Durr and R. Herges, THEOCHEM 1982, 6, 71-6.
Abstract:
The conformational behavior of cycloheptatriene and its valence isomer, norcaradiene, depends dramatically on the exocyclic angle at C-7. According to MINDO/3 calcns., the boat conformation exists in a flattened form, thus decreasing this angle. As a result, the equil. is shifted towards the cycloheptatriene valence isomer. The calcns. are used to explain previous exptl. data.
BibTeX:
@article{Durr1982,
author = {Durr, H. and Herges, R..},
title = {Cycloheptatriene/norcaradiene. Valence isomerization and conformational effects.},
journal = {THEOCHEM},
year = {1982},
volume = {6},
pages = {71-6},
doi = {http://doi.org/10.1016/0166-1280(82)80153-X}
}

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