Heterometallic clusters in homogeneous catalysis. Hydrogenation of diphenylacetylene and isomerization of cis-stilbene in the presence of [Fe 2Ru(CO) 12], [FeRu 2(CO) 12], [H 2FeRu 3(CO) 13], [H 2Ru 4(CO) 13], and related compounds. Identification of organometallic complexes and a discussion of their role

Abstract

The clusters [M 3(CO) 12], (M  Ru or Fe), [Fe 2Ru(CO) 12], [FeRu 2(C0) 12], [H 4Ru 4(CO) 12] and [H 2M′M 3(CO) 13] (M  Ru, M′  Fe or Ru) have been tested as homogeneous catalysts for the hydrogenation of C 2Ph 2 and isomerization of cis-stilbene. The effect of the cluster stoichiometry, of dihydrogen and of the substrate/cluster ratio have been evaluated. There is evidence of competition between dihydrogen, which favours the formation of catalytically active hydrides or “metal fragments”, and C 2Ph 2, which favours metal-fragment condensation to give alkyne-substituted clusters; with the exception of [H 2Ru 3(CO) 9C 2Ph 2], these derivatives are stable by-products and react slowly with dihydrogen, giving only small amounts of hydrogenation products. The alkyne-substituted derivatives found in the hydrogenation solutions are the reported products of the reactions of iron, ruthenium or iron-ruthenium carbonyl clusters with C 2Ph 2 under dinitrogen; however, there are differences in the yields. Moreover, in the reactions of [H 2Ru 4(CO) 13] or [H 2FeRu 3(CO) 13], a new derivative was obtained; this was characterized spectroscopically as a third isomer of [Ru 3(CO) 8(C 2Ph 2) 2].