Abstract Photoreduction of CO 2 to formate (HCO 2 − ) can be achieved by the phenazine-catalyzed system consisting of cobalt cyclam complex (Co-cyclam, cyclam = 1,4,8,11-tetraazacyclotetradecane) as an electron mediator and triethylamine as an electron donor. Flash photolysis revealed that the catalytic system should involve electron transfer from the photoformed radical anion of phenazine (P •− to Co III cyclam and hydrogen transfer from phenazinyl radical (P •− ) to intermediary Co II cyclam. The resulting cobalt hydride complex, Co-cyclam(H), provides formate through Co III formate complex formed by CO 2 insertion.