A reactive hydroxoferric porphyrazine complex, [(PyPz)Fe-III(OH) (OH2)](4+) (1, PyPz = tetramethyl-2,3-pyridino porphyrazine), has been prepared via one-electron oxidation of the corresponding ferrous species [(PyPz)Fe-II(OH2)(2)](4+) (2). Electrochemical analysis revealed a pH-dependent and remarkably high Fe-III-OH/Fe-II-OH2 reduction potential of 680 mV vs Ag/AgCl at pH 5.2. Nernstian behavior from pH 2 to pH 8 indicates a one-proton, one-electron interconversion throughout that range. The O-H bond dissociation energy of the Fe-II-OH2 complex was estimated to be 84 kcal mol(-1). Accordingly, 1 reacts rapidly with a panel of substrates via C-H hydrogen atom transfer (HAT), reducing 1 to [(PyPz)Fe-II(OH2)(2)](4+) (2). The second-order rate constant for the reaction of [(PyPz)Fe-III(OH) (OH2)](4+) with xanthene was 2.22 x 10(3) M-1 s(-1), 5-6 orders of magnitude faster than other reported Fe-III-OH complexes and faster than many ferryl complexes.