The binuclear compounds [H(CO)(PPh3)2Ru(M-bim)M(COD)] (bim = 2,2'-biimidazolate, COD = 1,5- cyclooctadiene, M = Rh, Ir) are more active catalysts for the reduction of cyclohexanone, styrene, and ,ß-unsaturated ketones (benzylideneacetophenone or benzylideneacetone), by hydrogen-transfer reactions from 2-propanol, than the mononuclear parent compounds [RuH(Hbim)(CO)(PPh3)2] and [M(Hbim)(COD)] (M = Rh, Ir). For the reduction of benzylideneacetone catalyzed by [H(CO)(PPh3)2Ru(/i-bim)Ir(COD)], the experimental kinetic data are in accordance with an expression of the form -d[benzylideneacetone]/df = k [Ru-Ir] [benzylideneacetone]. On the basis of these kinetic results and other experimental evidence, a mechanism for this reaction is proposed. The full catalytic cycle involves binuclear species. The hydrogen transfer proceeds via the ruthenium atom, while the iridium center acts as the core of a metal-ligand complex of variable electron density.

We thank the DGICYT (Projects PB 88-0386 and PB-89-0055, Programa de Promoción General del Conocimiento) for financial support.

Peer reviewed