Reactions of ruthenium-benzylidene complexes with bis(trimethylsilyl)ethene and trimethylsilylstyrenes: Olefin metathesis versus beta-SiMe3 elimination/reductive elimination

The benzylidene complexes [Cl-2(PCy3)(2)Ru=C(C6H4R-p)H] [R = H (1a), Cl (1b ), OMe (1c)] react with (E)-bis(trimethylsilyl)ethene (2) to give 3,3-bis(t rimethylsilyl)-1-arylprop-1-ene, H[H(SiMe3)(2)C]C=C(C6H4R-p)H (3a-c). Analo gously, reaction of la with trimethylsilylstilbene gives H(Ph)C=(SiMe3)H (4 a). In contrast, reaction of la with para-methoxysubstituted trimethylsilyl stilbene, H(Me3Si)C=C(C6H4OMe-p)H (4b), affords mixtures of the crossmetath esis product, H(Me3Si)C=C(Ph)H, and various propene derivatives. Labeling e xperiments have been carried out. The mechanism of these reactions is discu ssed.