[P,C]-Chelate Cobalt(III) Hydride Catalyzed Hydrosilylation of Alkenes

Bidentate ligand 2-diphenylphosphinobenzaldehyde or 2-diisopropyl­phosphino­benzaldehyde reacted with CoCl­(PMe3)3 to give [P,C]-chelate cobalt­(III) hydrides [mer-(Me3P)3Co­(H)­(Cl)­(o-Ph2P–C6H4–C═O)] (1) or [mer-(Me3P)3Co­(H)­(Cl)­(o-iPr2P–C6H4–C═O)] (2), respectively. Complex 2 was new and characterized by spectroscopic methods and single-crystal X-ray diffraction analysis. It was found that both complex 1 and 2 are active catalysts for hydrosilylation of alkenes. Although the catalytic activity of 1 is slightly higher, catalyst 1 and 2 have the same selectivity. The selectivity for aromatic alkenes is mainly of the Markovnikov type, while the selectivity for aliphatic alkenes is almost 100% anti-Markovnikov type. In the study of the reaction mechanism, a silyl cobalt dihydride [(Ph2ClSi)­Co­(H)2(PMe3)3] was isolated from the stoichiometric reaction of hydride 1 with Ph2SiH2. The catalytic mechanism for alkene hydrosilylation with [HCo­(PMe3)3] as a real catalyst is proposed and discussed with the experimental results.