Fast transfer hydrogenation using a highly active orthometalated heterocyclic carbene ruthenium catalyst

The free carbene 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene reacts with trans,cis-RuHCl(PPh3)2(ampy) (ampy = 2-(aminomethyl)pyridine) affording an orthometalated N-heterocyclic carbene complex characterized by an X-ray diffraction study. This compound in presence of NaOH shows very high catalytic activity for the transfer hydrogenation of several ketones to alcohols using 2-propanol as hydrogen source, affording TOF values up to 120,000 h−1 (at 50% conversion).