Mechanism of CO2 Reduction to Methanol with H2 on an Iron(II)-scorpionate Catalyst

CO2 utilization is an important process in the chemical industry with great environmental power. In this work we show how CO2 and H2 can be reacted to form methanol on an iron(II) center and highlight the bottlenecks for the reaction and what structural features of the catalyst are essential for efficient turnover. The calculations predict the reactions to proceed through three successive reaction cycles that start with heterolytic cleavage of H2 followed by sequential hydride and proton transfer processes. The H2 splitting process is an endergonic process and hence high pressures will be needed to overcome this step and trigger the hydrogenation reaction. Moreover, H2 cleavage into a hydride and proton requires a metal to bind hydride and a nearby source to bind the proton, such as an amide or pyrazolyl group, which the scorpionate ligand used here facilitates. As such the computations highlight the non-innocence of the ligand scaffold through proton shuttle from H2 to substrate as an important step in the reaction mechanism.