Solvent-Free Hydrosilylation of Alkenes Catalyzed by Well-Defined Low-Valent Cobalt Catalysts

A solvent-free cobalt-catalyzed highly selective hydrosilylation of alkenes has been developed. It was found that both Co(PMe3)(4) and CoCI(PMe3)(3) are highly active catalysts for hydrosilylation of alkenes. The former promoted Markovnikov-type hydrosilylation of the aryl alkenes, while the latter catalyzed anti-Markovnikov-type hydrosilylation of the alkyl alkenes. These two catalytic systems tolerate a variety of functional groups and provide high selectivity and medium to high yield. In the exploration of the reaction mechanism, a dinuclear silyl cobalt(I) complex [(PMe3)(2)Co(mu-eta(2)-HSiPh2)(2)Co(PMe3)(2)] (4) from the Co(PMe3)(4) system and a silyl cobalt dihydride [(PMe3)(3)Co(H)(2)SiClPh2] (5) from the CoCI(PMe3)(3) system were obtained. It is proposed that the silyl cobalt(I) intermediate, [Co(PMe3)(3)(SiHPh2)], is the real catalyst for the Co(PMe3)(4) system, while the hydrido cobalt(I) intermediate, [HCo(PMe3)(3)], is the real catalyst for the CoCI(PMe3)(3) system. Complexes 4 and 5 were characterized by spectroscopic methods and single-crystal X-ray diffraction.

Automated summary

A solvent-free cobalt-catalyzed highly selective hydrosilylation of alkenes has been developed using Co(PMe3)4 and CoCI(PMe3)3 as catalysts. The former promotes Markovnikov-type hydrosilylation of aryl alkenes, while the latter catalyzes anti-Markovnikov-type hydrosilylation of alkyl alkenes. These two catalytic systems exhibit good tolerance towards various functional groups, providing high selectivity and medium to high yield.