Theoretical Study of Flexible Molecular Systems Possessing Complexed Electronic Structure Towards Reaction Design and Control

运用电子结构理论对过渡金属催化的烯烃硅氢加成反应、二氧化碳加氢反应和Stille偶联反应进行了理论研究。Cp_2Zr对烯烃的硅氢加成反应不仅通过烯烃插入Zr-H键进行，而且还通过Zr-烯烃物种与氢硅烷之间的偶联反应进行。产物的释放不是简单的C-H和Si-C还原消除，而是烯烃辅助的还原消除和与氢硅烷的复分解。这些差异从后过渡金属催化的氢化硅烷化产生的d轨道能量差。从理论上阐明了水分子存在下Ru催化CO_2加氢反应的机理，水分子存在下，CO_2不是插入Ru-H，而是氢化物亲核进攻CO_2的碳中心，其活化能垒比通常的CO_2插入小得多。Stille偶联反应通过碘苯的氧化加成、金属间化合物的转移和还原消除进行。硫代甲烷是速率决定步骤，氟离子的存在加速了该步骤。从键能角度分析了其原因。

Theoretical Studies with electronic structure theory were carried out about hydrosilylation of alkene, hydrogenation of carbon dioxide, and Stille coupling reaction, which are typical transition-metal-catalyzed reaction. The hydrosilylation of alkene by Cp_2Zr takes place not only through alkene insertion into Zr-H bond but also coupling reaction between Zr-alkene species and hydrosilane. The product release step is not simple C-H and Si-C reductive elimination but alkene-assisted reductive eliminations and metathesis with hydrosilane. These differences from the late-transition-metal catalyzed hydrosilylation arise from the d orbital energy difference. Reaction mechanism of Ru-catalyzed hydrogenation of carbon dioxide was also theoretically elucidated in the presence of water molecule ; not the insertion of carbon dioxide into Ru-H but nucleophilic attack of hydride to carbon center of CO_2 takes place in the presence of water molecule, of which activation barrier is much smaller than usual CO_2 insertion. Stille coupling reaction takes place through oxidative addition of iodobenzene, transmetallation, and reductive elimination. Transmetallation is rate-determining step, which is accelerated by the presence of fluoride anion. The reason was discussed on the basis of bond energy.