Sc3+ (or HClO4) Activation of a Nonheme FeIII-OOH Intermediate for the Rapid Hydroxylation of Cyclohexane and Benzene.

[Fe(β-BPMCN)(CH3CN)2]2+ (1, BPMCN = N,N' -bis(pyridyl-2-methyl)- N,N' -dimethyl- trans-1,2-diaminocyclo-hexane) is a relatively poor catalyst for cyclohexane oxidation by H2O2 and cannot perform benzene hydroxylation. However, addition of Sc3+ activates the 1/H2O2 reaction mixture to be able to hydroxylate cyclohexane and benzene within seconds at -40 °C. A metastable S = 1/2 FeIII-(η1-OOH) intermediate 2 is trapped at -40 °C, which undergoes rapid decay upon addition of Sc3+ at rates independent of [substrate] but linearly dependent on [Sc3+]. HClO4 elicits comparable reactivity as Sc3+ at the same concentration. We thus postulate that these additives both facilitate O-O bond heterolysis of 2 to form a common highly electrophilic FeV═O oxidant that is comparably reactive to the fastest nonheme high-valent iron-oxo oxidants found to date.