Rhodium N-heterocyclic carbene complexes: Synthesis, structure, NMR studies and catalytic activity

The solid state structure, phosphine dissociation rates and catalytic activity of several Rh-N-heterocyclic carbene complexes were studied. Catalytic activity for the hydrogenation of β-methylstyrene was improved by up to two orders of magnitude upon the addition of copper chloride. The catalyst with the highest inherent activity was found to be [Rh(IMes)(P-p-FC6H4)3], although the p-methoxy derivative benefited the most from the addition of CuCl, giving turnover numbers of over 400 h−1.