CATALYSIS OF HYDROSILYLATION .28. THE ROLE OF DIOXYGEN IN HYDROSILYLATION OF ALKENES CATALYZED BY RUTHENIUM PHOSPHINE COMPLEXES

Catalytic hydrosilylation of C=C bonds in alkenes in the presence of Ru(II)-phosphine complexes takes place only for alkoxy-substituted silanes in the absence of solvent and in the presence of small amounts of O-2. The activation effect of ’’trace’’ O-2, noted previously for rhodium and other transition metal phosphine complex catalysts for several catalytic processes, has been little studied to date. In this work, oxygen is considered to cause removal of phosphine as its oxide, formation of intermediate dioxygen complexes (followed by oxygenation of Ru-Si= to an Ru-O-Si= moiety with elimination of disiloxane) and possible formation of Ru(IV) species. The studies include the characterization of isolated intermediates (well defined complexes or their mixtures) from an RuCl2(PPh(3))(3)-HSi(OC2H5)(3) system and general mechanisms for the hydrosilylation of alkenes in the presence of Ru(II) precursors are discussed.