Ruthenium-Catalyzed Formic Acid/Formate Dehydrogenation and Carbon Dioxide/(bi)carbonate Hydrogenation in Water

Abstract

The utilization of CO2 as a renewable C1 energy feedstock and efficient H2 storage and release using a molecular metal catalyst under milder reaction conditions in the aqueous phase remain a major challenge. Herein, we investigated a series of water-soluble (arene)Ru-pyridyloxime, -pyridylmethyloxime, and -pyridylimines complexes ([Ru]-1–[Ru]-8) for the catalytic formic acid (FA) dehydrogenation and CO2 hydrogenation in water under mild conditions. Among the studied complexes, the Ru-pyridyloxime catalyst exhibited high catalytic performance for reversible FA dehydrogenation, with a turnover number (TON) of ∼13,000 and remarkably high long-term stability (∼3 months) at 90 °C and CO2 hydrogenation with a cumulative TON of ∼133 and a formate yield of 0.97 mmol at 80 °C in water. To our delight, the same catalyst can efficiently hydrogenate bicarbonate and carbonate under analogous reaction conditions. Further, the Ru-pyridyloxime catalyst [Ru]-1 also exhibited reversible formate-CO2/(bicarbonate) dehydrogenation–hydrogenation in water. The in-depth mass and NMR investigations with control kinetic experiments revealed the involvement of several intermediate species and the pyridyloxime ligand in achieving the observed high catalytic activity over the [Ru]-1 catalyst.