CpRu(PPh3)2SSiiPr3与SCNR (R＝Ph, 1-Naphthyl)反应的结构、成键与机理的理论研究

应用密度泛函理论(DFT), 通过CpRu(PH₃)₂SSiⁱPr₃ (Cp＝环戊二烯负离子; ⁱPr＝异丙基)与SCNH模型化反应, 探讨了CpRu(PPh₃)₂SSiⁱPr₃ 与SCNR (R＝苯基, 萘基)的反应机理, 分析了反应所涉及的各相关化合物的结构与成键特征. 反应中首先失去一个膦配体, 生成一个中间体. 该中间体中, 硫原子采取sp²杂化, 硫原子剩余的一个p轨道与金属中心上的d轨道具有相同的对称性, 因而该p轨道上的孤电子对可与金属中心上的d轨道形成π键, 导致Cp环中心, Ru, S1, P和Si原子在同一平面内, 而不是S1, P和Si原子偏离该平面. 计算结果预测, S＝C双键中的p键打开, 生成含金属中心的四元环螯合物一步为反应的决速步骤. 空间位阻的减小、p共轭体系的生成以及螯合环的存在, 是导致该反应热力学有利的重要原因.

Theoretical Study of Structures, Bonding and Mechanism on Reaction of CpRu(PPh3)2SSiiPr3 with SCNR (R=Ph, 1-Naphthyl)

The model reaction mechanism of CpRu(PH₃)₂SSiⁱPr₃ with SCNH, derived from CpRu(PPh₃)₂- SSiⁱPr₃ with SCNR (R＝Ph, 1-naphthyl), was investigated by using density functional theory (DFT). The structures and bonding involved in the reaction mechanism were analyzed. The phosphine ligand is first dissociated from the reactant to afford an intermediate in the reaction. The sulphur atom in the intermediate has sp² hybridization, and the remaining p orbital is symmetrical to the d orbital of the metal center. Thus, the lone pair on the p orbital can have interaction with the d orbital to form a π bond, which leads to the coplanarity of the center of Cp ring, Ru, P, S and Si atoms, rather than the deviation of P, S and Si atoms from the plane. Our results of calculations predict that formation of a four-membered ring containing metal center is the rate-determining step. Decrease of steric hindrance, formation of p conjugation and occurrence of chelation are responsible for the favorable thermodynamics of the reaction.