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

Abstract

A series of half sandwich arene–ruthenium complexes [(η 6-arene)­RuCl­(κ 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, [(η 6-p-cymene)­RuCl­(κ 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.

Hydrogen Production from Formaldehyde and Paraformaldehyde in Water under Additive-Free Conditions: Catalytic Reactions and Mechanistic Insights

“…Recently, we have reported a series of arene-Ru­(II) complexes bearing bis-imidazole methane-based ligands for hydrogen gas production from formic acid in water and provided detailed mechanistic insights into the reaction pathway . Encouraged by these results and the rich literature reports regarding the high activity of imidazole based complexes in aqueous formic acid dehydrogenation, − herein, we have employed the arene-Ru­(II)-bis-imidazole methane-based complexes to produce hydrogen gas from HCHO-H 2 O solution under base-free and additive-free reaction conditions to achieve an impressive TON of >20,000 in 30 h at 90 °C.…”

Efficient and controlled H2 release from sodium formate

“…FA is reversibly regenerated from biomass processing or hydrogenation of carbon dioxide, and it is stable as a liquid under ambient conditions, which is favorable for portable devices. [16][17][18][19][20][21][22][23][24][25][26][27][28] Therefore, a large number of heterogeneous and homogeneous catalysts have been successfully explored for efficient H 2 evolution from FA via the dehydrogenation reaction (HCOOH → CO 2 + H 2 ), [29][30][31] avoiding CO production from FA dehydration (HCOOH → H 2 O + CO). [32][33][34] H 2 evolution upon FA dehydrogenation could be significantly improved by the addition of HCOONa to the system, 35,36 because FA dehydrogenation could be promoted by excess adsorbed HCOO − on the catalyst surface, which was suggested to be favorable for adsorption orientation of HCOOH (H-down).…”

Formic acid dehydrogenation by [Ru(η6-benzene)(L)Cl] catalysts: L = 2-methylquinolin-8-olate and quinolin-8-olate

“…20 Singh and the group have reported a series of half sandwich arene-ruthenium complexes with bis-imidazole methane-based ligands and achieved the highest TOF of 1545 h À1 . 21 The same group also employed a series of arene-ruthenium complexes with pyridine based ligands, and the most increased catalytic activity was observed with a TON of 6050. 22 Herein, the synthesis and characterisation of [Ru(Z 6benzene)(L)Cl] (In complex 1, L = 2-methyl 8-hydroxy quinoline, and in complex 2, L = 8-hydroxy quinoline) and its activity toward dehydrogenation of formic acid in the presence of sodium formate are depicted.…”

“…Singh and the group have reported a series of half sandwich arene–ruthenium complexes with bis-imidazole methane-based ligands and achieved the highest TOF of 1545 h −1 . 21 The same group also employed a series of arene–ruthenium complexes with pyridine based ligands, and the most increased catalytic activity was observed with a TON of 6050. 22…”