A High-Spin Iron(IV)–Oxo Complex Supported by a Trigonal Nonheme Pyrrolide Platform

We report the generation and characterization of a new high-spin iron­(IV)–oxo complex supported by a trigonal nonheme pyrrolide platform. Oxygen-atom transfer to [(tpa^Mes)­Fe^II]⁻ (tpa^Ar = tris­(5-arylpyrrol-2-ylmethyl)­amine) in acetonitrile solution affords the Fe­(III)–alkoxide product [(tpa^Mes2MesO)­Fe^III]⁻ resulting from intramolecular C–H oxidation with no observable ferryl intermediates. In contrast, treatment of the phenyl derivative [(tpa^Ph)­Fe^II]⁻ with trimethylamine N-oxide in acetonitrile solution produces the iron­(IV)–oxo complex [(tpa^Ph)­Fe^IV(O)]⁻ that has been characterized by a suite of techniques, including mass spectrometry as well as UV–vis, FTIR, Mössbauer, XAS, and parallel-mode EPR spectroscopies. Mass spectral, FTIR, and optical absorption studies provide signatures for the iron–oxo chromophore, and Mössbauer and XAS measurements establish the presence of an Fe­(IV) center. Moreover, the Fe­(IV)–oxo species gives parallel-mode EPR features indicative of a high-spin, S = 2 system. Preliminary reactivity studies show that the high-spin ferryl tpa^Ph complex is capable of mediating intermolecular C–H oxidation as well as oxygen-atom transfer chemistry.