Kinetics of reactions of hydrogen with [Os3(CO)11(NCMe)] and [Os3(CO)10(NCMe)2]

Abstract

The kinetics of reactions of [Os₃(CO)₁₁(NCMe)] with H₂ and CO, and of [Os₃(CO)₁₀(NCMe)₂] with H₂, have been studied in the presence of free MeCN. The reactions involve slow dissociation of MeCN from the clusters and subsequent competition between MeCN and H₂ or CO for the vacant co-ordination site on the intermediate cluster. Rate constants for nucleophilic attack on [Os₃(CO)₁₁] are in the order MeCN > PPh₃≈ CO > H₂ and temperature-dependence studies provide activation enthalpy and entropy differences. These, together with a value of 1.34 ± 0.03 for the deuterium kinetic isotope effect, are consistent with a simple three-centre transition state for reaction of [Os₃(CO)₁₁] with H₂. The cluster [Os₃H₂(CO)₁₀] reacts with MeCN to form [Os₃H₂(CO)₁₀(NCMe)] and equilibrium data for this reaction have been obtained.