Carbon Dioxide Catalyzed Cyclometallation of a Carbene Complex: Synthesis and Mechanism

The reaction of the nucleophilic carbene complex [Ph2P(S)(SO2Ph)C=Ru(p-cymene)] (1) with carbon dioxide is reported. Instead of forming an activation product by 1,2-addition of the C-O bond across the M=C bond, selective cyclometallation is observed. This metallation occurs at the phenyl group of the thiophosphoryl moiety and is thus in contrast to previously reported cyclometallations at the sulfonyl unit. DFT calculations demonstrate that the ease and selectivity of the reaction can be explained by a unique mechanism in which CO2 is coordinated by the carbene ligand. The thus formed carboxylate facilitates C-H activation and proton transfer to the former carbene center to re-liberate CO2.