Ruthenium based catalysts for olefin hydrosilylation: dichloro(p-cymene)ruthenium and related complexes

We report our third and final investigation into the use of ruthenium based compounds for catalyzing the hydrosilylation of methylvinyldimethoxysilane with methyldimethoxysilane. The catalytic mechanism of dichloro(p-cymene)ruthenium(II) (B1) is examined and compared to that of previously studied, less active catalysts. Density functional theory (DFT) has been applied to explore the possibility of fine-tuning the catalytic ability of B1. The eta(6)-ligand and the sigma-donor ligands were varied to assess the steric and electronic factors that affect the reactivity of the catalyst. The catalytic ability is diminished by increasing the size of the eta(6)-ligand (p-cymene replaced by 1,3,5-cyclooctatriene) or the sigma-donor strength of the other ligands (chloride replaced by methyl). The original catalyst (B1) appears to strike an optimum balance with regard to the sigma-donor capabilities of the ligands as it is able to interconvert relatively freely between the Ru(II) and Ru(IV) oxidation states. All catalytically active compounds benefit from an initial exchange of one of the sigma-donor ligands for a hydride ligand in the induction step.