Reaction of Cp2(CH3)Ta=CH2 with Ru3(CO)12: deoxygenative coupling of carbon monoxide and methylene units to give a heteronuclear cluster-bound 4-cumulene ligand

Abstract

The mechanisms of reactions that deoxygenate carbon monoxide (CO) and convert it into longer-chain hydrocarbons are not well understood. A reaction is reported between an early metal methylidene complex and a late transition metal carbonyl species that results in CO deoxygenation along with coupling of the CO carbon to methylidene groups and other CO carbons. The Schrock tantalum-methylene complex (η5-C5H5)Ta(=CH2)(CH3) reacts with the trinuclear metal carbonyl species Ru3(CO)12 to yield the cluster complex Cp2(CH3)Ta(µ-O)Ru3(C4H4)(CO)9. This material contains a 4-cumulene ligand that bridges the three late-metal centers. Also formed in this reaction is the unstable free tantalum oxo species, (η5-C5H5)Ta(=O)(CH3). A crystal structure of the TaRu3 cluster is reported along with a proposed mechanism for this unusual carbon–carbon bond-forming reaction. Keywords: deoxygenation, carbon monoxide, alkylidene, coupling, cluster.