Olefins asymmetric hydrosilation

The recent discovery that a chiral phosphine ligand in a platinum(II) complex can give rise to a catalytic asymmetric hydrosilation of prochiral olefins seems to prove that a phosphine ligand can be included in the coordination sphere of platinum in an active catalytic species, but that when a phosphine ligand is so included, the activity of the species is reduced by several orders of magnitude. 

Asymmetric hydrosilation of prochiral olefins other than 1,1-disubsti-tuted ones was unsuccessful because they were unreactive under the conditions employed. Styrene afforded a 20% yield of 1-phenylethyl- and 50% of 2-phenylethylmethyldichlorosilane, both inactive. The 1-phenylethyl isomer had a possibility of activity with its asymmetric center, PhMeC HSi=. 

Another recent report described the asymmetric hydrosilation of styrene using chiral phosphine ligands such as methyldiphenylphosphine 160). Enantiomeric excesses of 5% of S isomer of 2-phenylethyl-trichlorosilane were obtained. The mechanism almost certainly involved insertion of Pd(II) into a silicon-hydride bond, followed by addition of Pd-hydride across the olefinic bond and elimination of Pd(II) to give the silicon-carbon bond. 

Asymmetric induction has been observed in the hydrosilation of prochiral olefins with optically active complexes as catalysis. See I. Ojima, K. Yamamoto, and M. Kumada, Aspects Homogen. Catal. 3, 185 (1977). 

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