Coupling vs. metathesis of vinylsiloxanes catalyzed by Ru-complexes

Effective disproportionation of vinylsiloxanes (vinylmethylbis(trimethylsiloxy)silane (I) and vinyltris(trimethylsiloxy)silane (II)) proceeds in the presence of ruthenium(II) complexes, e.g., RuHCl(CO)(PPh3)(3) and RuCl2(PPh3)(3) in air to yield new E-bis(siloxy)ethenes, (except the RuHCl(CO)(PPh3)(3) catalyzed reaction of (I) giving 1:1 mixture of E-l,2-bis(siloxy)ethene and 1,1-bis(siloxy)ethene). The reaction can be regarded as a molecular model of a new method of poly(methyl, vinyl)siloxanes cross-linking. Cross-coupling of the two vinylsiloxanes (I) and (II) with styrene also effectively catalyzed by Ru-complexes allows a synthesizing of new E-l-phenyl-2-(siloxy)ethenes. Mechanistic implications following from the previous works assume the involvement of Ru-H and Ru-Si intermediates responsible for catalytic reactions. beta-Si transfer to metal from a beta-siloxyethyl ligand bonded to Ru atom is a key step in the homocoupling of vinylsiloxane and its heterocoupling with olefin (styrene). (C) 1998 Elsevier Science B.V. All rights reserved.