Diruthenium Catalyst for Hydrogen Production from Aqueous Formic Acid

A dirutheniummolecular catalyst exhibited high catalyticactivity compared to those of analogous mononuclear ruthenium catalystsfor hydrogen production from formic acid in water with high long-termstability over 60 days, affording a turnover number of 93 200. Diruthenium complexes [{(eta(6)-arene)-RuCl}(2)(mu-kappa(2):kappa(2)-benztetraimd)](2+) containing the bridging bis-imidazolemethane-based ligand{1,4-bis-(bis-(2-ethyl-5-methyl-1H-imidazol-4-yl)-methyl)-benzene}(benztetraimd) are synthesized for catalytic formic acid dehydrogenationin water at 90 degrees C. Catalyst [{(eta(6)-p-cymene)-RuCl}(2)(mu-kappa(2):kappa(2)-benztetraimd)](2+) [1-Cl ( 2 ) ] exhibited a remarkably high turnoverfrequency (1993 h(-1) per Ru atom) and long-term stabilityover 60 days for formic acid dehydrogenation, while the analogous(eta(6)-benzene)-diruthenium and mononuclear catalystsdisplayed low activity with poor long-term stability. Notably, catalyst [1-Cl ( 2 ) ] also displayedan appreciably high turnover number of 93 200 for the bulk-scalereaction. In addition, the in-depth mass and nuclear magnetic resonanceinvestigations under the catalytic and control experimental conditionsrevealed the active involvement of several crucial catalytic intermediatespecies, such as Ru-aqua species [{(eta(6)-p-cymene)-Ru-(H2O)}(2)(mu-L)](2+) [1-(OH ( 2 ) ) ( 2 ) ], Ru-formato species[{(eta(6)-p-cymene)-Ru-(HCOO)}(2)(mu-L)] [1-(HCOO) ( 2 ) ], and Ru-hydrido species [{(eta(6)-p-cymene)-Ru-(H)}(2)(mu-L)] [1-(H) ( 2 ) ], in the catalyticformic acid dehydrogenation reaction.