Cross-Metathesis of Vinylsilanes with Styrene Catalyzed by Ruthenium−Carbene Complexes

The cross-metathesis of styrene with various vinylsilanes, H 2 C C(H)SiR 3, catalyzed by [Cl 2 (PCy 3 ) 2 Ru CHPh] ( 1 ) to give ( E )-silylstyrene, ( E )-Ph(H)C C(H)SiR 3, and ethylene is reported. The reaction proceeds even at room temperature and is highly selective. Very high conversions are observed when R = OEt, OSiMe 3 (≥95%, 6 h, 2 mol % of 1) . The conversion significantly decreases with increasing substitution of Me for OR‘. The metathesis is reversible. Therefore, removal of ethylene is critical for achieving high conversions. From the study of stoichiometric reactions of 1 with vinylsilanes it follows that in the series SiR 3 = Si(OEt) 3, SiMe(OEt) 2, SiMe 2 OEt, SiMe 3 and SiR 3 = Si(OSiMe 3 ) 3, SiMe(OSiMe 3 ) 2, SiMe 2 (OSiMe 3 ), SiMe 3 the conversion rate increases, but simultaneously the selectivity of the metathesis decreases. The decreasing selectivity readily accounts for the decreasing efficiency in the catalytic metathesis. The product distribution of reactions of styrene- d 8 with H 2 C C(H)SiR 3 (R = OEt, OSiMe 3 ) in the presence of 1 provides evidence for a metallacarbene mechanism involving [Ru] CHPh and [Ru] CH 2 species.