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 r uthenium(II), rhodium(III), and iridium(III) are connected via three chloro bridges to RuCl2(PPh3)(2), have been synthesized. The complexes were obtai ned 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 stabi lizing 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 ha ve been structurally characterized. The abilities of all the complexes to c atalyze the oxidation of secondary alcohols with 2-butanone have been inves tigated. The complex [Cp* Rh(mu -Cl)(3)RuCl(PPh3)(2)] has proved to be high ly active, displaying a performance superior to that of previously known ca talysts 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 poten tial of these types of bimetallic complexes to act as catalysts for other r eactions is discussed.