Half-sandwich chloro complexes as ligands for RuCl2L2 (L = PR3, alkene):: Syntheses, structures, and catalytic activity of new homo- and heterobimetallic complexes

Homo- and heterobimetallic complexes, in which half-sandwich complexes of ruthenium(II), rhodium(III), and iridium(III) are connected via three chloro bridges to RuCl2(PPh3)(2), have been synthesized. The complexes were obtained in quantitative yields by reaction of [(cymene)RuCl(mu -Cl)](2) or [Cp*MCl(mu -Cl)](2) (M = Rh, Ir) with [(PPh3)(2)ClRu(mu -Cl)(3)Ru(Me2CO)(PPh3)(2)] (2). The crystal structure of 2 has been determined by X-ray analysis. Evidence that half-sandwich chloro complexes are generally suited for stabilizing RuCl2L2 fragments is provided by the synthesis of complexes [(cymene)Ru(mu -Cl)(3)RuCl(dppb)] [dppb =1,4-bis (diphenylphosphanyl)butane] and [(cymene)Ru(mu -Cl)(3)RuCl(cod)] (cod = 1,5-cyclooctadiene), both of which have been structurally characterized. The abilities of all the complexes to catalyze the oxidation of secondary alcohols with 2-butanone have been investigated. The complex [Cp* Rh(mu -Cl)(3)RuCl(PPh3)(2)] has proved to be highly active, displaying a performance superior to that of previously known catalysts such as [RuCl2(PPh3)(3)]. Using a substrate/catalyst ratio of 500:1, initial turnover frequencies of up to 3400 h(-1) were observed. The potential of these types of bimetallic complexes to act as catalysts for other reactions is discussed.