A theoretical study on the hydrogenation of CO 2 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 [RuH 2 (Me 2 PCH 2 SiMe 2 ) 2 NH(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 H 2 activation strategy in the hydrogenation of CO 2 to methanol may not be the methanol-assisted H 2 activation, but the formate-assisted H 2 activation. In this cascade reaction, all energy spans of stage I, II and III are 20.2 kcal mol -1 of the formate-assisted H 2 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 [RuH 2 (Me 2 PCH 2 SiMe 2 ) 2 NH(CO)], [RuH 2 (Ph 2 PCH 2 SiMe 2 ) 2 NH(CO)] and [RuH 2 (Me 2 PCH 2 SiMe 2 ) 2 NH(CO)] exhibit similar catalytic activities for the hydrogenation of CO 2 to methanol.