Catalytic hydrogenation of carbon dioxide to methanol by homogenous ruthenium(ii) hydrido carbonyl complexes

Abstract

Ruthenium(II) hydrido carbonyl complexes, namely, [RuH(CO)(CH₃CN)₂(PPh₃)₂]⁺X⁻ [X = BF₄ (1) and PF₆ (2)], were synthesized and characterized spectroscopically. The molecular structure of 2 was determined by the single-crystal X-ray diffraction technique. The structure study of 2 revealed that it is a mononuclear complex with a ruthenium centre and distorted octahedral geometry. These complexes were used as catalysts towards the catalytic hydrogenation of CO₂ to methanol at 90 °C in an integrated one-pot system, where methanol was obtained in high yields in acidic media. Among the two ruthenium-based catalysts, 1 showed superior catalytic performance over 2 owing to the varying proton-accepting abilities of their counterions, which also affected the catalytic rate. Thus, its superior catalytic performance makes [RuH(CO)(PPh₃)₂(CH₃CN)₂]BF₄ a potential candidate for realizing the large-scale production of methanol by CO₂ hydrogenation. We also conclude that for the scalable conversion of CO₂ to methanol, aluminum tris(trifluoromethanesulfonate) acid results in the highest catalytic activity when compared with other acids.