Chelation Numbers Differentiate Performances of Co(II) Macrocyclic Catalysts in Electro-/Photocatalytic CO2 Reduction.

Mechanistic studies with characterizing crucial intermediates are indispensable in elucidating the promotive effects of ligand modifications, which thereby serve as useful orientations for rational optimization of molecular catalysts for CO₂ reduction. Herein we investigate the catalytic mechanism of a Co^II catalyst bearing a tetra-dentate macrocyclic ligand by electrochemical and spectroelectrochemical techniques, where its unstable Co⁰ active species under catalytic conditions accounts for its lower catalytic performance compared to that of another Co^II catalyst featuring a similar penta-dentate macrocyclic ligand.