Iron-oxidation-state-dependent O–O bond cleavage of meta-chloroperbenzoic acid to form an iron(IV)-oxo complex

The mechanism of formation of [FeIV(O)(N4Py)]2+ (2, N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) from the reaction of [FeII(N4Py)(CH3CN)]2+ (1) with m-chloroperbenzoic acid (mCPBA) in CH2Cl2 at −30 °C has been studied on the basis of the visible spectral changes observed and the reaction stoichiometry. It is shown that the conversion of 1 to 2 in 90% yield requires 1.5 equiv. peracid and takes place in two successive one-electron steps via an [FeIII(N4Py)OH]2+(3) intermediate. The first oxidation step uses 0.5 equiv. peracid and produces 0.5 equiv. 3-chlorobenzoic acid, while the second step uses 1 equiv. peracid and affords byproducts derived from chlorophenyl radical. We conclude that the FeII(N4Py) center promotes O–O bond heterolysis, while the FeIII(N4Py) center favors O–O bond homolysis, so the nature of O–O bond cleavage is dependent on the iron oxidation state.