Cross-metathesis vs. silylative coupling of vinyl alkyl ethers with vinylsilanes catalyzed by a ruthenium-carbene complex (Grubbs catalyst)

Grubbs complex, (PCy3)(2)Cl2Ru=CHPh (I) is a very effective catalyst of the cross-disproportionation of vinyl-trisubstituted silanes H2C=CHSiR3 [where R-3=Me-3, PhMe2, (OEt)(3)] with vinyl alkyl ethers H2C=CHOR' [where R'=ethyl, propyl, butyl, t-butyl, t-pentyl, 2-(ethyl)hexyl, cyclohexyl, trimethylsilyl] to yield a mixture of (E+Z) 1-silyl-2-alkoxyethenes. The reaction occurs quantitatively under milder conditions (60 degrees C) than the analogous one catalyzed by Ru-H and/or Ru-Si complexes reported previously (80 degrees C)(7) The stoichiometric reaction of (I) and (PCy3)(2)Cl2Ru=CH2 (III) with vinyl ethyl ether leads to the formation of (PCy3)(2)Cl2Ru=CH(OEt) (II), inactive in the stoichiometric reaction with vinylsilanes but very active in the catalytic process. Experiments with the use of deuterated vinylsilanes indicate the non-metallacarbene mechanism of the reaction and provide evidence for the initiation of Ru-H bond formation via the hydrovinylation with vinylsilanes.