Room Temperature Formate Ester Transfer Hydrogenation Enables an Electrochemical-Thermal Organometallic Cascade for Methanol Syn-thesis from CO2

The reduction of CO2 to synthetic fuels is at the core of energy storage efforts. However, the formation of energy-dense liquid fuels such as methanol remains a major challenge, particularly under low temperature and pressure conditions that can be coupled to renewable electricity sources via electrochemistry. A multicatalyst system pairing an electrocatalyst with a thermal organometallic catalyst is introduced here, enabling the room temperature reduction of 1 atmosphere of CO2 to methanol. The reaction sequence involves: (i) the reduction of CO2 to formate by the electrocatalyst [Cp*Ir(bpy)Cl]+ (bpy = 2,2’-bipyridine), (ii) Fischer esterification of formate to isopropyl formate catalyzed by trifluoromethanesulfonic acid (HOTf), and (iii) thermal transfer hydrogenation of isopropyl formate to methanol facilitated by the organometallic catalyst (H-PNP)Ir(H)3 (H-PNP = bis[(2-diisopropyl-phosphino]ethyl)amine). Reaction development led to mutually compatible conditions for a one-pot CO2 reduction in isopropanol electrolyte at ambient temperature and 1 atmosphere CO2. The isopropanol solvent plays sever-al crucial roles: activating formate ion as isopropyl formate, donating hydrogen for the reduction of formate ester to methanol via transfer hydrogenation, and lowering the barrier for transfer hydrogenation through hydrogen bonding interactions. In addition to reporting a method for room temperature reduction of challenging ester substrates, this work provides a proto-type for pairing electrochemical and thermal organometallic reactions that can guide the design and development of multi-catalyst cascades.