Journal of Cluster Sc&nce, Vol. 3, No. 4, 1992 Organometallic Chemistry and Homogeneous Catalysis of Rh and Rh-Co Mixed Metal Carbonyl Clusters Iwao Ojima, 1 Robert J. Donovan, 1 Patrizia Ingallina, 1 Nfria Clos, 1 William R. Shay, 1 Masakatsu Eguehi, 1 Qingping Zeng, 1 and Anna Korda 1 Received November 6, 1992 The reactions of hydrosilane and/or alkyne as well as isonitriles with rhodium and rhodium-cobalt mixed metal carbonyl clusters, e.g., Rh4(CO)I 2 and CozRh2(CO)l 2, are studied. Novel mixed metal complexes, e.g., CoRh(CO)5 (HC~CBun), (R3Si)2Rh(CO)nCo(CO)4, Rh(R N=-C)4Co(CO)4 , C02Rh 2 (CO)Io(HC-=CR), and CozRhz(CO)9(HC=-CBu"), are synthesized and identified. The catalytic activities of these rhodium and rhodium-cobalt mixed metal complexes are examined in hydrosilylation, silylformylation, and novel silylcarbocyclization reactions. Possible mechanisms for these reactions are proposed and discussed. KEY WORDS: Rhodium carbonyl clusters; rhodium-cobalt carbonyl clusters; homogeneous catalysis; hydrosilylation; silylformylation; silylcarbocyclization. INTRODUCTION Mixed metal clusters have high potential to serve as efficient catalysts for variety of homogeneous catalytic reactions as well as unique reagents for organic syntheses. Following the identification of CoRh(CO)7 as an active catalytic species in the hydroformylation-amidocarbonylation of penta- fluorostyrene catalyzed by mixed-metal systems of cobalt and rhodium [1], we have been investigating the catalytic activity and reactions of Co2Rh2(CO)I 2 and CoRh(CO)7 to explore unique properties of these mixed-metal systems. It has been shown that reactions of Co2Rh2(CO)12 with nucleophiles such as carbon monoxide [-2, 3], phosphines [4-71, phosphites 1-5,8], and 1 Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400. 423 1040-7278/92/1200-0423506.50/0 © 1992PlenumPublishing Corporation