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

Abstract

The cross-metathesis of styrene with various vinylsilanes, H 2 CdC(H)SiR 3 , catalyzed by [Cl 2 (PCy 3 ) 2 RudCHPh] (1) to give (E)-silylstyrene, (E)-Ph(H)CdC(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 (g95%, 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 Cd C(H)SiR 3 (R ) OEt, OSiMe 3 ) in the presence of 1 provides evidence for a metallacarbene mechanism involving [Ru]dCHPh and [Ru]dCH 2 species.

Cross-metathesis of vinylsilanes with olefins in the presence of Grubbs’ catalyst

“…All reactions proceeded highly stereoselectively with a strong preference for the formation of the E isomer. The reactions of vinylsilanes with substituted styrenes 7 as well as with the unsubstituted styrene and with allyltrimethylsilane even afforded exclusively (within detection limits) the E isomer.…”

“…6 Recently, we reported on the high catalytic activity of Grubbs' catalyst in the cross-metathesis of vinylsilanes and vinylsiloxanes with styrene (Scheme 2). 7 High yields and selectivities were obtained for vinyltrialkoxyand vinyltrisiloxysilanes under very mild conditions (room temp. ).…”

“…9 Products were isolated and characterized spectroscopically. Since vinylsilanes were found to be inactive for the conversion to self-metathesis products, 7 the vinylsilanes could be used in excess. Thus, it was possible to minimize the role of competitive olefin self-metathesis.…”

“…Similar results were obtained in the reactions with styrene. 7 Removal of ethylene was found to be crucial for an increase of reaction efficiency. 7 A high metathesis conversion was achieved by effective stirring and heating of the reaction mixture in CH 2 Cl 2 to a gentle reflux.…”

“…7 Removal of ethylene was found to be crucial for an increase of reaction efficiency. 7 A high metathesis conversion was achieved by effective stirring and heating of the reaction mixture in CH 2 Cl 2 to a gentle reflux. All reactions proceeded highly stereoselectively with a strong preference for the formation of the E isomer.…”