Acidp K a Dependence inO–O Bond Heterolysis of a Nonheme Fe III –OOH IntermediateTo Form a Potent Fe V O Oxidant with Heme CompoundI‑Like Reactivity

Protons play essential roles in natural systems in controlling O–O bond cleavage of peroxoiron(III) species to give rise to the high-valent iron oxidants that carry out the desired transformations. Herein, we report kinetic and mechanistic evidence that acids can control the mode of O–O bond cleavage for a nonheme S = 1/2 FeIII–OOH species [(BnTPEN)FeIII(OOH)]2+ (2, BnTPEN = N-benzyl-N,N′,N′-tris(2-pyridylmethyl)-1,2-diaminoethane). Addition of acids having pKa values of >8.5 in CH3CN results in O–O bond homolysis, leading to the formation of hydroxyl radicals that give rise to alcohol/ketone (A/K) ratios of around 1 in the oxidation of cyclohexane. However, the introduction of acids with pKa values of <8.5 elicits a different outcome, namely the achievement of A/K ratios of as high as 9, the observation of rapid and catalytic hydroxylation of cyclohexane, and a million-fold acceleration in the decay rate of the FeIII–OOH intermediate at −40 °C. These results implicate the generation of a highly reactive ...