The oxidation of a series of hydrocarbons by the nonheme iron(IV)-oxo complex [(N4Py)FeIV═O]2+ is efficiently mediated by N-hydroxyphthalimide. The increase of reactivity is associated to the oxidation of the mediator to the phthalimide N-oxyl radical, which efficiently abstracts a hydrogen atom from the substrates, regenerating the mediator in its reduced form.