Intermolecular trapping of a nonheme Fe(IV)=O intermediate

The reactions of Fe-III(TPA) (TPA = tris(2-pyridylmethyl)amine) complexes with 2-methyl-1-phenyl-2-propyl-hydroperoxide (MPPH) delivered by syringe pump under anaerobic conditions afford nearly quantitative conversion of MPPH to products derived from the benzyl radical. These results unequivocally show that MPPH breaks down by O-O bond homolysis, leading to the formation of the benzyl radical and a high valent Fe(IV)=O species. Without added substrates, the benzyl radical reacts with the high valent species to form benzyl alcohol or benzyl halides. The Fe(IV)=O species can also effect the two-electron oxidation of added substrates such as thioanisole, cyclohexanol, and cyclooctene under appropriate conditions. The oxidation of thioanisole and cyclohexanol is likely facilitated by pre-equilibrium binding of the substrate to the metal center, allowing these substrates to intercept the high valent iron-oxo species as it forms. These results suggest the importance of close proximity to direct the high valent metal center down a desired pathway.