Oxoferryl species are commonly proposed as intermediates in catalytic cycles, especially biological systems in which O activation is required. Diatomic oxygen has a high reduction potential (E = 1.23 V), but the first step required to harness this potential is a thermodynamically unfavorable one electron reduction E = -0.16 V. This reduction occurs in nature by the formation of a superoxide complex in which a reduced metal is oxidized by O. The product of this reaction is a peroxide radical that is more readily reactive. A widely applicable method for the generation of high-valent oxoferryl species is the oxidation with iodosobenzene: