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.

Key words: density functional theory, reaction mechanism, ruthenium complex, silyl migration