Fe(TPA)-catalyzed alkane hydroxylation can be a metal-based oxidation

The hydroxylation of cyclohexane by t-butyl hydroperoxide using [Fe2O(TPA)(2)(H2O)(2)](4+) (1, TpA=tris(2 pyridylmethyl)amine) as the catalyst has been investigated with the use of a syringe pump to control the concentration of the alkyl hydroperoxide. Unlike an alkoxy radical-based radical chain autoxidation mechanism, the reaction observed produces only alcohol (no ketone) with a deuterium kinetic isotope effect of 10, similar to heme-catalyzed hydroxylations. An alkylperoxoiron(III) intermediate can be trapped at -40 degrees C and characterized by a number of spectroscopic methods. A mechanistic scheme is proposed involving this intermediate which either serves as the precursor to the metal-based oxidant or oxidizes the substrate directly.