Chromium-catalyzed transfer hydrogenation of CO2 to formate using isopropanol under ambient pressure†

Herein, we present the first example of earth-abundant 3d metal-catalyzed ambient pressure carbon dioxide transfer hydrogenation to formate using isopropanol as an inexpensive and environmentally benign hydrogen source. The bidentate phosphine bis(diphenylphosphino)propane (DPPP, β_n = 91°)-derived low-valent Cr(0) complex Cr(DPPP)(CO)₄C- emerged as the most efficient catalyst yielding sodium formate with a TON of up to 1974 under 1 bar CO₂ and 2231 under 5 bar CO₂ in the presence of NaOH in a THF : H₂O mixture after 24 h at 130 °C. The catalyst was also found to be active in the transfer hydrogenation of sodium bicarbonate and carbonate to produce their corresponding formates in low yields. Mechanistic experiments revealed formation of an anionic hydride complex, which is believed to be an active catalyst for CO₂ transfer hydrogenation.