Substitution kinetics of [Os3(CO)11(NCMe)] and [Os3(CO)10(NCMe)2]

Abstract

The kinetics of reactions of [Os₃(CO)₁₁(NCMe)] and [Os₃(CO)₁₀(NCMe)₂] with P- or As-donor ligands in p-xylene or toluene have been studied and shown to be characteristic of reversible dissociative processes. In both cases MeCN is ca.10 times more nucleophilic towards the reactive intermediate than is PPh₃. Activation parameters confirm the weakness of the Os–NCMe bonds and suggest that loss of the first MeCN from [Os₃(CO)₁₀(NCMe)₂] may be a concerted process in which a ‘sideways on’ bridging CO replaces the leaving MeCN. The strength of bridge bonding can be estimated to be 30 kJ mol^–1.