Reactivity of Dinuclear and Tetranuclear Clusters of Molybdenum and Tungsten

Abstract

The reactivity of dinuclear and tetranuclear clusters of molybdenum and tungsten are reviewed with particular attention to oxidative addition and reductive elimination sequences. Principles pertaining to the design of a catalytic system are discussed in light of the above and specific attention is given to the hydrogenation and isomerization of alkenes by W4(H)2(OPri)14. Recent studies of the reductive coupling and selective cross coupling of ketones/aldehydes to olefins are presented in their reactions with W2(OR)6(py)2 compounds. A two step mechanism is proposed based on the initial cleavage of the C-O double bond to give an alkylidene bridged oxo compound followed by further reaction with aldehyde or ketone. A pinacol coupling is ruled out. Recent studies of the activation of carbon monoxide by W2(OR)6 and W4(OR)12 clusters are presented with the latter providing the first example of the stoichiometric cleavage of C≡O to carbide and oxide ligands on a cluster.