Ruthenium(II) Complexes Bearing a Pyridyl-Supported Pyrazolyl−N-Heterocyclic Carbene (NNC) Ligand and Their Catalytic Activity in the Transfer Hydrogenation of Ketones

Ruthenium(II) complexes bearing a pyridyl-supported pyrazol-3-yl−N-heterocyclic carbene (NNC) ligand were synthesized from the reactions of RuCl3·3H2O with pyridyl-supported pyrazol-3-yl−imidazolium salts in the presence of carbon monoxide. These Ru(II) complexes have exhibited good to excellent catalytic activity in the transfer hydrogenation of ketones in refluxing 2-propanol. Formation of a coordinatively unsaturated Ru(II) center in the precatalyst is attributed to the high catalytic activity of the Ru(II) complexes.