A Highly Active Ruthenium(II) Pyrazolyl-Pyridyl-Pyrazole Complex Catalyst for Transfer Hydrogenation of Ketones

Ruthenium(II) complexes bearing a pyrazolyl-pyridyl-pyrazole ligand were synthesized and exhibited exceptionally high catalytic activity in the transfer hydrogenation of ketones in refluxing isopropyl alcohol, reaching final TOFs up to 720 000 h(-1). The beta-NH functionality of the pyrazole arm in the ligand demonstrated a remarkable acceleration effect on the reaction rate. The unsymmetrical nature (hemilability) and presence of the convertible NH group of the ligand is attributed to the high catalytic activity of the complex catalyst.