Ligand-tuned catalytic activity of ruthenium-imidazolyl amine complexes for reversible formic acid dehydrogenation and CO2 hydrogenation to formic acid

Formic acid (FA) dehydrogenation was investigated over several arene-ruthenium catalysts with various imidazolyl-, thiophenyl- and furyl-based ligands. The catalyst with an N-((1H-imidazol-2-yl)methyl)propan-2-amine ligand (Ru/L7) outperformed other catalysts in FA dehydrogenation at 90 degrees C in water. Furthermore, the developed process was scaled up by a factor of 10 without any loss in activity. Remarkably, Ru/L7 exhibited high robustness and long-term durability during reusability over 79 catalytic runs, achieving very high turnovers per Ru, releasing 37.6 L of gas (H2 and CO2) with a productivity rate of 15 660 L(H2+CO2) molRu-1 h-1 (similar to 7 gH2 gRu-1 h-1). Advantageously, the Ru/L7 catalyst also promoted CO2 hydrogenation to formate at 80 degrees C. Mechanistic insights were gained through KIE studies and via the identification of several catalytic intermediates involved in various steps of catalytic FA dehydrogenation and CO2 hydrogenation under catalytic and controlled reaction conditions.