Homogeneous catalytic hydrosilylation of the CC double bond with platinum catalysts

Hydrosilylation of vinyl- and vinylidene-type olefins (styrene (1a), 2-phenyl-propene (1b), methyl methacrylate (6)) has been carried out with either PtCl2 (dissolved in the substrate) or a platinum-phosphine catalyst prepared in situ. The activity and regioselectivity of the platinum-phosphine catalysts depend strongly on the phosphine structure and the metalligand ratio. Complexes involving chelating phosphines are inactive. Although mainly linear regioisomers are formed (2 and 7 respectively) in the reaction of 6, some 1,4-addition of the silane to the conjugated system also takes place to give a silyl ketene acetal derivative (8). A marked decrease in the reaction rate is observed if Ph3SiH instead of Et3SiH is used as the hydrosilylating agent.