Cyclohexene as a substrate probe for the nature of the high-valent iron-oxo oxidant in Fe(TPA)-catalyzed oxidations

Cyclohexene is shown to be a versatile substrate probe in shedding light on the nature of the high-valent oxidant generated by bio-inspired nonheme iron catalysts. Cyclohexene provides the oxidant a choice to attack an allylic C-H bond or a CC bond, and the selectivity observed should depend on the electronic properties of the oxidant. Allylic oxidation products are predominantly observed in the reaction with [Fe^IV(O)(TPA)(NCCH₃)]²⁺ (TPA = tris(2-pyridylmethyl)amine), while epoxide and cis-diol are the major products found in the [Fe^II(TPA)(NCCH₃)₂] ²⁺-catalyzed reaction with H₂O₂. This difference suggests that the oxidant generated in the latter case must be distinct from [Fe^IV(O)(TPA)(NCCH₃)]²⁺ and supports an oxoiron(v)-hydroxo species that has been proposed as the oxidant.