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

Abstract

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 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.

CO2 Reduction by an Iron(I) Porphyrinate System: Effect of Hydrogen Bonding on the Second Coordination Sphere

“…The cumulative emission of CO 2 is raising environmental concerns for its role in global warming, and consequently CO 2 reduction is an urgent global issue. In the face of these serious environmental problems, the capture of CO 2 has become a hot issue in recent years. − However, apart from CO 2 capture and storage, research has started into the utilization of CO 2 for the synthesis of valuable chemicals and materials. − Because CO 2 is a cheap, abundant, and nontoxic C 1 feedstock, it can be converted into various carbon resources such as alcohols, acids, esters, and hydrocarbons. − This approach has 2-fold advantages, namely, CO 2 reduction in the atmosphere as well as reduction in the use of unrenewable fossil fuels for synthesis of these compounds. Therefore, transforming CO 2 into valuable chemicals may provide a solution to not only environmental problems caused by the emission of CO 2 but also the anticipated depletion of fossil resources.…”