Dicobalt diporphyrin complex with hyperfine EPR spectrum mediates only a two-electron reduction of O2

A dicobalt diporphyrin complex can form μ-superoxo dimer with O2 in chloroform in the absence of organic base to give 15-line highly symmetrical EPR spectrum. This complex can only catalyze O2 reduction by a two-electron pathway, suggesting that there is no correlation between the shape of the Co–O2–Co EPR signal and the electrocatalytical ability of dicobalt diporphyrin complexs to mediate the four-electron reduction of O2.