Selective CO2 Electroreduction to CO by an Organometallic Nickel Catalyst Featuring a C3–Symmetric Tris(Phosphino)Alkyl Ligand

We report a Nickel CO2 reduction electrocatalyst based on a C3-symmetric tris(phosphino)alkyl ligand, CNPPh3, which displays a metalated axial carbon atom. Catalyst NiHBr selectively reduces CO2 to CO (FYCO = 94%) at −2.3 V vs Fc+/0 with a TO Fmax = 65 s–1 in DMF/[TBA]PF6 with 3.5 M of added H2O. Cyclic voltammetry (CV) and an exhaustive computational study of the reaction mechanism show that our NiII complex undergoes two one-electron reduction events before the CO2 binding step. Afterward, the catalytic CO2 reduction takes place through a reduction-first pathway. The formation of a Ni–CO intermediate along the CO2 reduction pathway was inferred by CV, and the corresponding [NiII–CO]+ complex was isolated. FTIR spectroelectrochemistry (SEC) allowed for the detection of three different Ni–CO species: [Ni–CO]+, [Ni–CO]0, and [Ni–CO]−. This work provides critical insights into the electrocatalytic CO2 reduction, laying the foundation for efficient CO2 conversion strategies.