Half-Sandwich Chloro Complexes as Ligands for RuCl2L2 (L = PR3, alkene): Syntheses, Structures, and Catalytic Activity of New Homo- and Heterobimetallic Complexes

Abstract

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(μ-Cl)]2 or [Cp*MCl(μ-Cl)]2 (M = Rh, Ir) with [(PPh3)2ClRu(μ-Cl)3Ru(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(μ-Cl)3RuCl(dppb)] [dppb = 1,4-bis(diphenylphosphanyl)butane] and [(cymene)Ru(μ-Cl)3RuCl(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(μ-Cl)3RuCl(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.