Abstract
We demonstrate that bench-stable ruthenium-PNP nitrosyl complex salts with different counteranions (Cl(-), BF(4) (-), BPh(4) (-), PF(6) (-), and OTs(-)) and a ruthenium-POP nitrosyl complex are competent (pre)-catalysts for the CO(2) hydrogenation to formic acid (FA) at low temperatures in ionic liquids. Only a minor effect of variation of the counteranion was observed, and weakly basic ionic liquids such as EMIM OAc, BMIM OAc, and EMIM HCO(2) were suitable for this transformation, affording conversions up to 94 mol % formic acid compared to the ionic liquid (FA/IL) and turnover numbers (TONs) up to 1305. Importantly, the same catalytic system was also efficient for the dehydrogenation of formic acid back to CO(2) and H(2), affording conversions up to >95% (949 TON) after 3 h at 95 °C. To investigate the application of such protocols for hydrogen storage and transportation purposes, hydrogenation/dehydrogenation cycles were performed, showing that this new catalytic system can promote up to 10 reversible CO(2) hydrogenation/FA dehydrogenation cycles before losing its activity.