A theoretical study on the hydrogenation of CO2 to methanol catalyzed by ruthenium pincer complexes.

Herein, a density functional theory (DFT) study was performed to investigate thoroughly the cascade reaction mechanism for the hydrogenation of carbon dioxide to methanol catalyzed by ruthenium pincer complex [RuH2(Me2PCH2SiMe2)2NH(CO)]. Three catalytic stages involving the hydrogenation of carbon dioxide (stage I), formic acid (stage II) and formaldehyde (stage III) were studied. The calculated results show that the dominant H2 activation strategy in the hydrogenation of CO2 to methanol may not be the methanol-assisted H2 activation, but the formate-assisted H2 activation. In this cascade reaction, all energy spans of stage I, II and III are 20.2 kcal mol-1 of the formate-assisted H2 activation. This implies that it could occur under mild conditions. Meanwhile, the catalyst is proposed to be efficient for the transfer hydrogenation using isopropanol as the hydrogen resource, and the ruthenium pincer complexes [RuH2(Me2PCH2SiMe2)2NH(CO)], [RuH2(Ph2PCH2SiMe2)2NH(CO)] and [RuH2(Me2PCH2SiMe2)2NH(CO)] exhibit similar catalytic activities for the hydrogenation of CO2 to methanol.