Ruthenium(II) Complexes of an Imidazole Carboxamido Ligand for Base-Free Transfer Hydrogenation in Air

Two half-sandwich ruthenium(II) complexes of an imidazole-2-carboxamido ligand have been synthesized and characterized by nuclear magnetic resonance spectroscopy, elemental analysis, and, in one case, single-crystal X-ray diffraction. Both complexes serve as precatalysts for base-free transfer hydrogenation under aerobic conditions. A substrate scope study with a range of ketones and aldehydes was performed, and a preliminary investigation into the mechanism of catalysis was undertaken. These complexes represent relatively rare examples of transfer hydrogenation catalysts that do not require an inert atmosphere and an exogenous base.