Rhodium Complexes Bearing 1,10-Phenanthroline Analogue Bis-NHC Ligands Are Active Catalysts for Transfer Hydrogenation of Ketones

Synthesis of a new example of the pyridazine annelated bis(N-heterocyclic carbene) ligand 3b (vegi) bearing benzyl substituents is reported, as well as the synthesis of its cationic Rh(cod) complex 5b . The mechanism of formation of the [Rh(cod)(vegi)] + complexes was investigated, showing a stepwise deprotonation of the imidazolium moieties via the mono-carbene imidazolium Rh(cod)Cl species 4 . The [Rh(cod)(vegi)] + complexes 5a, b show catalytic activity in the transfer hydrogenation of even sterically hindered ketones.