Diruthenium Catalyst for Hydrogen Production from Aqueous Formic Acid.

Diruthenium complexes [{(η-arene)RuCl}(μ-κ:κ-benztetraimd)] containing the bridging bis-imidazole methane-based ligand {1,4-bis(bis(2-ethyl-5-methyl-1-imidazol-4-yl)methyl)benzene} (benztetraimd) are synthesized for catalytic formic acid dehydrogenation in water at 90 °C. Catalyst [{(η--cymene)RuCl}(μ-κ:κ-benztetraimd)] exhibited a remarkably high turnover frequency (1993 h per Ru atom) and long-term stability over 60 days for formic acid dehydrogenation, while the analogous (η-benzene)diruthenium and mononuclear catalysts displayed low activity with poor long-term stability. Notably, catalyst also displayed an appreciably high turnover number of 93 200 for the bulk-scale reaction. In addition, the in-depth mass and nuclear magnetic resonance investigations under the catalytic and control experimental conditions revealed the active involvement of several crucial catalytic intermediate species, such as Ru-aqua species [{(η--cymene)Ru(HO)}(μ-L)] , Ru-formato species [{(η--cymene)Ru(HCOO)}(μ-L)] -, and Ru-hydrido species [{(η--cymene)Ru(H)}(μ-L)] , in the catalytic formic acid dehydrogenation reaction.