Diruthenium Catalyst for Hydrogen Production from Aqueous Formic Acid.

Diruthenium complexes [{(η 6 -arene)RuCl} 2 (μ-κ 2 :κ 2 -benztetraimd)] 2+ containing the bridging bis-imidazole methane-based ligand {1,4-bis(bis(2-ethyl-5-methyl-1 H -imidazol-4-yl)methyl)benzene} (benztetraimd) are synthesized for catalytic formic acid dehydrogenation in water at 90 °C. Catalyst [{(η 6 - p -cymene)RuCl} 2 (μ-κ 2 :κ 2 -benztetraimd)] 2+ [1-Cl 2 ] exhibited a remarkably high turnover frequency (1993 h -1 per Ru atom) and long-term stability over 60 days for formic acid dehydrogenation, while the analogous (η 6 -benzene)diruthenium and mononuclear catalysts displayed low activity with poor long-term stability. Notably, catalyst [1-Cl 2 ] 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 6 - p -cymene)Ru(H 2 O)} 2 (μ-L)] 2+ [1-(OH 2 ) 2 ] , Ru-formato species [{(η 6 - p -cymene)Ru(HCOO)} 2 (μ-L)] [1 - (HCOO) 2 ] , and Ru-hydrido species [{(η 6 - p -cymene)Ru(H)} 2 (μ-L)] [1-(H) 2 ] , in the catalytic formic acid dehydrogenation reaction.