Department of Chemistry, Hacettepe University, Ankara 06800, Turkey.
J Phys Chem A. 2008 May 22;112(20):4636-43. doi: 10.1021/jp076044c.
A catalytic system consisting of tungsten carbene generated from WCl(6) and an atomic carbon is investigated theoretically for the metathesis of 1-octene at B3LYP/extended LANL2DZ level of DFT. The ground-state geometries and charge distributions of the structures belonging to the reaction mechanism are located. Energetics for the complete set of reactions, involving the formation of the tungsten carbene precatalyst, Cl(4)WCCl(2), the formation of tungsten methylidene and tungsten heptylidene with this precatalyst, and finally productive and degenerative metathesis steps with these alkylidene species are calculated in terms of total electronic energy and thermal energies. The free-energy (ΔG(298)) surfaces of the structures involved in the related reactions are constructed. In addition, solvent effects on the single point energies of the structures are investigated for two different solvents, namely, cyclohexane and chloroform. The results indicate that the formation of the catalytically active heptylidene is energetically favored in comparison to the formation of methylidene, while the degenerative and productive metathesis steps are competitive. In the catalytic cycle, the formation of ethylene is exothermic, while the formation of 7-tetradecene is endothermic. As expected, solvent effects on the metathesis reactions are minor and solvation does not cause any change in the directions of the overall metathesis reactions.
在 B3LYP/扩展 LANL2DZ 密度泛函理论水平上，理论研究了由 WCl(6)和原子碳生成的钨卡宾组成的催化体系在 1-辛烯复分解反应中的应用。定位了属于反应机制的结构的基态几何形状和电荷分布。涉及钨卡宾前催化剂的形成，Cl(4)WCCl(2)，前催化剂形成钨亚甲基和钨庚基以及最后与这些亚烷基物种进行生产性和退化复分解步骤的完整反应的能量，是根据总电子能和热能计算的。构建了相关反应涉及的结构的自由能（ΔG(298)）表面。此外，还研究了两种不同溶剂环己烷和氯仿对结构单点能的溶剂效应。结果表明，与形成亚甲基相比，催化活性庚基的形成在能量上是有利的，而退化和生产性复分解步骤是竞争的。在催化循环中，乙烯的形成是放热的，而 7-十四烯的形成是吸热的。正如预期的那样，溶剂对复分解反应的影响较小，溶剂化不会引起整体复分解反应方向的任何变化。
