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1.
Alexander Zeller 《Journal of organometallic chemistry》2006,691(21):4379-4385
The ethylene polymerization reaction of a neutral nickel catalyst was studied by DFT calculations at the Becke3LYP/6-31G(d) level of theory. As in related cases a β-agostic bond stabilizes the nickel alkyl ground states. Transition states for the insertion of the olefin show a distinct α-agostic interaction, which has not been observed for late metal polymerization catalysts before. An ethylene-alkyl complex was identified as the resting state of the reaction. The overall barrier height of the reaction amounts to 17.54 kcal/mol, which slightly increases to 17.60 kcal/mol for the polymerization of deuterated ethylene. Therefore, a small positive kinetic isotope effect (kH/kD = 1.09) can be calculated, which is caused by the α-agostic interaction in the transition state. A comparison to other late metal based polymerization systems reveals that the ethylene coordination step of highly active catalysts is significantly lower in energy compared to catalysts which are only moderately active. 相似文献
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A. Holle G. Wiebusch J. Main K. H. Welge G. Zeller G. Wunner T. Ertl H. Ruder 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1987,5(4):279-285
For deuterium Rydberg atoms in a magnetic field of ~6 T we compare the complete experimental spectrum in the range ?190 cm?1 to ?20 cm?1 with the positions and oscillator strengths of the corresponding quantum theoretically calculated photoabsorption lines. The agreement is excellent. The range of energy covered extends from the end of thel-mixing regime up to the regions where the approximate integrability of the problem is completely lost, and the corresponding classical system undergoes a transition to chaos. 相似文献
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Statistical methods are applied to the theoretical study of the kinetics of the thermal degradation of crosslinked polycondensates. The parameters required by the theory are the crosslinking degree, the molecular weight of monomers, and the number of free chain ends of the polymer sample. There is a good agreement between theoretical results and experimental data obtained by isothermal thermogravimetric analysis of specially synthesized s-triazinic polycondensates. 相似文献
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al-Ktaifani MM Bauer W Bergsträsser U Breit B Francis MD Heinemann FW Hitchcock PB Mack A Nixon JF Pritzkow H Regitz M Zeller M Zenneck U 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(11):2622-2633
Several independent synthetic routes are described leading to the formation of a novel unsaturated tetracyclic phosphorus carbon cage compound tBu4C4P6 (1), which undergoes a light-induced valence isomerization to produce the first hexaphosphapentaprismane cage tBu4C4P6 (2). A second unsaturated isomer tBu4C4P6 (9) of 1 and the bis-[W(CO)5] complex 13 of 1 are stable towards similar isomerization reactions. Another starting material for the synthesis of the hexaphosphapentaprismane cage tBu4C4P6 (2) is the trimeric mercury complex [(tBu4C4P6)Hg]3 (11), which undergoes elimination of mercury to afford the title compound 2. Single-crystal X-ray structural determinations have been carried out on compounds 1, 2, 9, 11, and 13. 相似文献
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5-Amino-4-cyano-1-(hetero)arylimidazoles 1 are prepared by reaction of N-(hetero)arylformimidoethylesters 2 with 2-aminomalodinitrile in acetic acid. 相似文献
10.
Marija R. Zoric Usha Pandey Kadel Kirill A. Korvinson Hoi Ling Luk Arunpatcha Nimthong‐Roldan Matthias Zeller Ksenija D. Glusac 《Journal of Physical Organic Chemistry》2016,29(10):505-513
The conformational flexibility of three covalently linked dimers consisting of two xanthene‐based moieties connected by a diphenyl ether linker was studied using NMR spectroscopy, X‐ray crystallography, and density functional theory (DFT) calculations. The three dimers interconvert as a function of pH: the doubly cationic dimer (Xan+)2 exists in acidic solutions (pH < 0.5), the mono‐alcohol monocation Xan+–Xan‐OH at intermediate pH values (pH = 1–3), and the neutral diol at the highest pH‐values (pH > 3). Each dimer exhibits conformational degrees of freedom associated with rotations of either the xanthene moiety or of the diphenyl ether (DPE) linker. The barriers for rotation of the xanthylium moiety were evaluated using DFT calculations, yielding values of 23 kcal/mol for (Xan+)2 and 11 kcal/mol for (Xan‐OH)2, respectively. The rotational barrier for the diphenyl ether linker in Xan+–Xan‐OH (15 kcal/mol) was experimentally determined using variable temperature NMR measurements. The relative orientation of the two –OH groups in (Xan‐OH)2 diol was investigated in solution and the solid state using NMR spectroscopy and X‐ray crystallography. The conformer observed in the solid state was found to be the In–Out conformer, while free rotation of the xanthenol units is thought to occur on the NMR timescale at room temperature. These studies are relevant for the design of linkers for efficient water oxidation catalysts. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献