Nonheme Iron Mediated Oxidation of Light Alkanes with Oxone: Characterization of Reactive Oxoiron(IV) Ligand Cation Radical Intermediates by Spectroscopic Studies and DFT Calculations

The oxidation of light alkanes that is catalyzed by heme and nonheme iron enzymes is widely proposed to involve highly reactive {Fe-V=O} species or {Fe-IV=O} ligand cation radicals. The identification of these high-valent iron species and the development of an iron-catalyzed oxidation of light alkanes under mild conditions are of vital importance. Herein, a combination of tridentate and bidentate ligands was used for the generation of highly reactive nonheme {Fe=O} species. A method that employs [Fe-III(Me(3)tacn)(Cl-acac)Cl](+) as a catalyst in the presence of oxone was developed for the oxidation of hydrocarbons, including cyclohexane, propane, and ethane (Me(3)tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane; Cl-acac = 3-chloro-acetylacetonate). The complex [Fe-III(Tp)(2)](+) and oxone enabled stoichiometric oxidation of propane and ethane. ESI-MS, EPR and UV/Vis spectroscopy, O-18 labeling experiments, and DFT studies point to [Fe-IV(Me(3)tacn)({Cl-acac}(center dot+))(O)](2+) as the catalytically active species.