Mechanism of Olefin Hydrosilylation Catalyzed by RuCl₂(CO)₂(PPh₃)₂: A DFT Study

Density functional theory (DFT) was used to explore the different mechanistic possibilities for the hydrosilylation reaction between methyldimethoxysilane and methylvinyldimethoxysilane catalyzed by the Ru(II) complex dicarbonyldichlorobis(triphenylphosphine)ruthenium(II) ( A1 ). Reaction enthalpy profiles of the Chalk−Harrod, modified Chalk−Harrod, and σ-bond metathesis mechanisms were computed for several different active forms of A1 . A total of 10 different pathways with different catalytic cycles and different induction steps were compared. We predict that a σ-bond metathesis mechanism involving the formation of a hydride analogue of A1 is most favored, in contrast to the commonly accepted Chalk−Harrod mechanism of hydrosilylation. The B3LYP-calculated activation energy within the catalytic cycle (Δ H act = 21.8 kcal/mol) is small enough to make A1 a reasonable catalyst for this reaction under the normally applied experimental conditions.