Kinetics and Mechanism of Oxidative Addition and Reductive Elimination of Hydrogen on Triruthenium Clusters

The kinetics of the reversible reaction HRu₃(μ-COMe)(CO)₁₀ + H₂ <=* H₃Ru₃(μ₃-COMe)(CO)₉ + CO has been studied. The reaction of H₃Ru₃(M₃-COMe)(CO)₉ with carbon monoxide has a rate law which is first order in metal cluster and zero order in carbon monoxide pressure; on the basis of the rate law, activation parameters, and deuterium kinetic isotope effect, the rate-determining step is proposed to be reductive elimination of molecular hydrogen through a three-center transition state. The reaction of HRu₃(μ₃-COMe)(CO) ₁₀ with hydrogen involves dissociation of a carbonyl ligand prior to the rate-determining step, which is proposed to be the oxidative addition of molecular hydrogen. The relative rates for reactions of the unsaturated intermediate HRu₃(COMe)(CO)₉ with hydrogen and with carbon monoxide were determined. Comparisons between these results and studies of metal surfaces and of mononuclear metal complexes are discussed.