© 2016 American Chemical Society. In the search for the two-electron-reduced intermediate of the tetraaza catalyst [CoIIN4H(MeCN)]2+(N4H = 2,12-dimethyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),2,11,13,15-pentaene) for CO2reduction and elementary steps that result in the formation of CO product, rapid-scan FT-IR spectroscopy of the visible-light-sensitized catalysis, using Ir(ppy)3in wet acetonitrile (CD3CN) solution, led to the observation of two sequential intermediates. The initially formed one-electron-reduced [CoIN4H]+-CO2adduct was converted by the second electron to a transient [CoIN4H]+-CO2-complex that spontaneously converted CO2to CO in a rate-limiting step on the second time scale in the dark under regeneration of the catalyst (room temperature). The macrocycle IR spectra of the [CoIN4H]+-CO2-complex and the preceding one-electron [CoIN4H]+-CO2intermediate show close similarity but distinct differences in the carboxylate modes, indicating that the second electron resides mainly on the CO2ligand. Vibrational assignments are corroborated by13C isotopic labeling. The structure and stability of the two-electron-reduced intermediate derived from the time-resolved IR study are in good agreement with recent predictions by DFT electronic structure calculations. This is the first observation of an intermediate of a molecular catalyst for CO2reduction during the bond-breaking step producing CO. The reaction pathway for the Co tetraaza catalyst uncovered here suggests that the competition between CO2reduction and proton reduction of a macrocyclic multi-electron catalyst is steered toward CO2activation if the second electron is directly captured by an adduct of CO2and the one-electron-reduced catalyst intermediate.