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

Bigi, Julian P., Harman, W. Hill, Lassalle-Kaiser, Benedikt, Robles, Damon M., Stich, Troy A., Yano, Junko, Britt, R. David, Chang, Christopher J.
Journal of the American Chemical Society 2012 v.134 no.3 pp. 1536-1542
Fourier transform infrared spectroscopy, X-ray absorption spectroscopy, absorption, acetonitrile, electron paramagnetic resonance spectroscopy, iron, mass spectrometry, oxidation, trimethylamine
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 [(tpaᴹᵉˢ)Feᴵᴵ]⁻ (tpaᴬʳ = tris(5-arylpyrrol-2-ylmethyl)amine) in acetonitrile solution affords the Fe(III)–alkoxide product [(tpaᴹᵉˢ²ᴹᵉˢᴼ)Feᴵᴵᴵ]⁻ resulting from intramolecular C–H oxidation with no observable ferryl intermediates. In contrast, treatment of the phenyl derivative [(tpaᴾʰ)Feᴵᴵ]⁻ with trimethylamine N-oxide in acetonitrile solution produces the iron(IV)–oxo complex [(tpaᴾʰ)Feᴵⱽ(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 tpaᴾʰ complex is capable of mediating intermolecular C–H oxidation as well as oxygen-atom transfer chemistry.