Bis-Imidazole Methane Ligated Ruthenium(II) Complexes: Synthesis, Characterization, and Catalytic Activity for Hydrogen Production from Formic Acid in Water

A series of half sandwich arene-ruthenium complexes [(eta(6)-arene)RuCl(kappa(2)-L)](+) ([Ru]-1-[Ru]-10) containing bis-imidazole methane-based ligands {4,4'-(phenylmethylene)bis( 2- ethyl- 5- methyl- 1H- imidazole)} ( L1), {4,4'-(( 4-methoxyphenyl)methylene)bis( 2-ethyl-5-methyl-1H-imidazole)} (L2), {4,4'-((2-methoxyphenyl)methylene)bis(2-ethyl-5-methyl-1H-imidazole)} (L3), {4,4'-((4- chlorophenyl)methylene)bis(2-ethyl-5-methyl-1H-imidazole)} (L4), and {4,4'-((2-chlorophenyl)methylene)bis(2-ethyl-5-methyl-1H-imidazole)} (L5) are synthesized. The synthesized and purified complexes ([Ru]-1-[Ru]-10) are further employed for hydrogen production from formic acid in aqueous medium. Among the investigated complexes, [(eta(6)-pcymene)RuCl(kappa(2)-L2)](+) [Ru]-2, having Ru(II) coordinated 4-methoxy phenyl substituted bis-imidazole methane ligand (L2), outperformed over others, displaying a higher catalytic turnover of 8830 and high efficiency (TOF = 1545 h(-1)) with appreciably high long-term stability for formic acid dehydrogenation in water.

Automated summary

A series of half sandwich arene-ruthenium complexes containing bis-imidazole methane-based ligands were synthesized and tested for hydrogen production from formic acid in aqueous medium. Among the complexes investigated, Ru(II) coordinated with a 4-methoxyphenyl substituted bis-imidazole methane ligand exhibited the highest catalytic turnover and efficiency for formic acid dehydrogenation in water.