Selective CO ₂ Electroreduction to CO by an Organometallic Nickel Catalyst Featuring a C ₃ –Symmetric Tris(Phosphino)Alkyl Ligand

We report a Nickel CO₂ reduction electrocatalyst based on a <i>C</i> ₃-symmetric tris-(phosphino)-alkyl ligand, CNPPh₃, which displays a metalated axial carbon atom. Catalyst <b>Ni</b> ^<b>H</b> _<b>Br</b> selectively reduces CO₂ to CO (FY_CO = 94%) at -2.3 V vs Fc^+/0 with a TO <i>F</i> _max = 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 Ni^II 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 [Ni^II-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.