Dimeric Ruthenium(II)-NNN Complex Catalysts Bearing a Pyrazolyl-Pyridylamino-Pyridine Ligand for Transfer Hydrogenation of Ketones and Acceptorless Dehydrogenation of Alcohols

Dimeric pincer-type ruthenium­(II)-NNN
complexes bearing an unsymmetrical
pyrazolyl-pyridylamino-pyridine ligand were prepared and characterized
by NMR, elemental analysis, and X-ray single crystal structural determination.
These complexes exhibited very high catalytic activity for both transfer
hydrogenation of ketones and acceptorless dehydrogenation of secondary
alcohols, achieving TOF values up to 1.9 × 106 h–1 in the transfer hydrogenation of ketones. The high
catalytic activity of the Ru­(II) complex catalysts is attributed to
the presence of the unprotected NH functionality in the ligand and
hemilabile unsymmetrical coordination environment around the central
metal atoms in the complex.