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

Abstract

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 °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) mol_Ru⁻¹ h⁻¹ (∼7 g_H2 g_Ru⁻¹ h⁻¹). Advantageously, the Ru/L7 catalyst also promoted CO₂ hydrogenation to formate at 80 °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.