Metallocene complexes of type Cp'2MCH(TMS)(2) (Cp' =eta(5)-Me5C5, M = Y, Sm), Me2SiCp2"SmCH(TMS)(2) (Cp" =eta(5)-Me4C5) catalyze rapid and clean hydrosilylation of CH2=CH-SiMe2R (R = Me, Ph, NMe2, O'Bu) with PhSiH3. The distribution of 1,2-addition product versus 2, 1-addition product was found to be sensitive to both catalysts and substrates. Generation of 2, 1-addition product can best be achieved by use of more sterically accessible catalysts as well as substrates containing tethering functional groups. A. four-centered transition state is invoked to explain these effects. [GRAPHICS] (c) 2005 Elsevier B.V. All rights reserved.