Formylation-Decarbonylation Relay Strategy for the Selective Hydrogenation of CO2 to CO.

We report here an alternative approach to conducting the reverse water-gas shift (RWGS) reaction catalyzed by a ruthenium pincer complex and an amine. In this strategy, a secondary amine is first formylated by CO2 and H2 to make H2O and formamide. The formamide then undergoes decarbonylation to produce CO with the concomitant regeneration of the amine. Both steps, formylation and decarbonylation, were independently investigated through catalytic optimization studies and DFT computations at the PBE0-D3-(BJ)PCM(THF)/def2-TZVP level. Using morpholine and Ru-MACHO pincer catalyst, a TON of 249 was achieved for the hydrogenation of CO2 to CO (at 70 bar, 170 °C for 90 h) with 100% selectivity.