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.