Mechanism of the sequential activation of two C–H bonds of a NHC N-methyl group on a triruthenium carbonyl cluster

Abstract

Recent experimental studies on metal complexes of N-heterocyclic carbenes (NHCs) showed a few examples of the unique sequential activation of two C–H bonds of NHC N-methyl group on triruthenium carbonyl clusters. However, the corresponding theoretical calculations showed that the reactions are highly endergonic (>40 kcal/mol) and involve very high barriers (up to ~80 kcal/mol), failing to rationalize the experimental observations that the reactions were carried out under mild conditions (<100 °C). The present work re-examines a representative example of the sequential activation of the two C–H bonds with the aid of density functional theory calculations. From the present results, the reaction is predicted to be endergonic by only 14.7 kcal/mol with an overall barrier of 35.1 kcal/mol, which is in good agreement with the experimental observations that the reaction smoothly proceeds under thermal reaction conditions and that the reversed transformation from the product to reactant occurs when carbon monoxide was gently bubbled into the reaction system at room temperature.