Bubbling O-2 into a THE solution of CoH(BDPP) (1) at -90 degrees C generates an O-2 adduct, Co(BDPP)(O-2) (3). The resonance Raman and EPR investigations reveal that 3 contains a low spin cobalt(III) ion bound to a superoxo ligand. Significantly, at -90 degrees C, 3 can react with 2,2,6,6-tetramethyl-1-hydroxypiperidine (TEMPOH) to form a structurally characterized cobalt(III)-hydroperoxo complex, Co-III(BDPP)(OOH) (4) and TEMPO center dot. Our findings show that cobalt(III)-superoxo species are capable of performing, hydrogen atom abstraction processes. Such a stepwise O-2-activating process helps to rationalize cobalt-catalyzed aerobic oxidations and sheds light on the possible mechanism of action for Co-bleomycin.