Cross-metathesis of vinylsilanes with styrene catalyzed by ruthenium-carbene complexes

The cross-metathesis of styrene with various vinylsilanes,H2C=C(H)SiR3, cat alyzed by [Cl-2(PC(y)3)(2)Ru=CHPh] (1) to give (E)-silylstyrene, (E)-Ph(H)C =C(H)SiR3, and ethylene is reported. The reaction proceeds even at room tem perature and is highly selective. Very high conversions are observed when R = OEt, OSiMe3 (greater than or equal to 95%, 6 h, 2 mol % of 1). The conve rsion significantly decreases with increasing substitution of Me for OR'. T he 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 SiR3 = Si(OEt)(3), SiMe(O Et)(2), SiMe2OEt, SiMe3 and SiR3 = Si(OSiMe3)(3), SiMe(OSiMe3)(2), SiMe2(OS iMe3), SiMe3 the conversion rate increases, but simultaneously the selectiv ity of the metathesis decreases. The decreasing selectivity readily account s for the decreasing efficiency in the catalytic metathesis. The product di stribution of reactions of styrene-d(s) with H2C= C(H)SiR3 (R = OEt, OSiMe3 ) in the presence of 1 provides evidence for a metallacarbene mechanism inv olving [Ru]=CHPh and [Ru]=CH2 species.