Mechanism of olefin hydrosilylation catalyzed by [RuCl(NCCH₃)₅]⁺: a DFT study

The hydrosilylation reaction between methyldimethoxysilane and methylvinyldimethoxysilane, catalyzed by the cationic species chloropenta(acetonitrile)ruthenium(II)⁺ (C1), was investigated with density functional theory (DFT). The Chalk-Harrod, Glaser-Tilley and σ-bond metathesis mechanisms were considered as mechanistic possibilities for the reaction and enthalpy profiles of each pathway were computed for the active form of C1. In contrast to the commonly accepted Chalk-Harrod mechanism of hydrosilylation, the computational results indicate that a σ-bond metathesis mechanism, involving the formation of a hydride analogue of C1, is most favored. The B3LYP calculated activation enthalpy for this pathway (ΔH_act = 13.1 kcal/mol) is consistent with the experimental observation that C1 is a reasonable catalyst for this reaction under the applied experimental conditions.