*S Supporting Information

1(7),2,11,13,15-pentaene) was used for electrocatalytic CO2 reduction in wet MeCN with a glassy carbon working electrode. When water was employed as the proton source (10 M in MeCN), CO was produced ( f CO = 45 % ± 6.4) near the Co I/0 redox couple for [CoIIIN4H(Br)2] + (E1/2 = −1.88 V FeCp2+/0) with simultaneous H2 evolution ( fH2 = 30 % ± 7.8). Moreover, we successfully demonstrated that the catalytically active species is homogeneous through the use of control experiments and XPS studies of the working glassy-carbon electrodes. As determined by cyclic voltammetry, CO2 catalysis occurred near the formal Co I/0redox couple, and attempts were made to isolate the triply reduced compound (“[Co0N4H]”). Instead, the doubly reduced (“Co I”) compounds [CoN4] and [CoN4H(MeCN)] + were isolated and characterized by X-ray crystallography. Their molecular structures prompted DFT studies to illuminate details regarding their electronic structure. The results indicate that reducing equivalents are stored on the ligand, implicating redox noninnocence in the ligands for H2 evolution and CO2 reduction electrocatalysis. Transition metal complexes supported by nitrogen-donor ligands constitute an important class of molecular electro-catalysts for CO2reduction. 1 Wherea