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

The mechanism of formation of [Fe(IV)(O)(N4Py)](2+) (2, N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) from the reaction of [Fe(II)(N4Py)(CH(3)CN)](2+) (1) with m-chloroperbenzoic acid (mCPBA) in CH(2)Cl(2) 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 [Fe(III)(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 Fe(II)(N4Py) center promotes O-O bond heterolysis, while the Fe(III)(N4Py) center favors O-O bond homolysis, so the nature of O-O bond cleavage is dependent on the iron oxidation state.