Models for Peroxidase Compound I: Generation and Spectroscopic Characterization of New Oxoferryl Porphyrin π Cation Radical Species

Oxoferryl porphyrin ir cation radical species have been generated by the oxidative action of m-chloroperoxybenzoic acid on the triflato complexes of [tetrakis(2, 6-dichlorophenyl)porphyrinato]- and [tetrakis(2, 4, 6-trimethoxyphenyl)-porphyrinato]-iron(III) in methylene chloride/methanol-d₄. The new high-valent complexes have been characterized by a variety of spectroscopic techniques and compared to the oxoferryl porphyrin π cation radical complex generated from [tetramesitylporphyrinato]iron(III) triflate. The UV-vis and ¹H NMR spectra of the oxidized species are qualitatively similar. In the EPR, the complexes all show ferromagnetic coupling between ferryl and porphyrin x cation radical spins yielding quartet states. However, the average effective g values of the xy EPR transitions, (g_{x, y}^eff), indicate that spin coupling is not as strong as assumed in earlier studies. A self-consistent set of parameters D, D/E, J° and J^d has been derived for the tetramesityl- and tetrakis(2, 6-dichlorophenyl)porphyrin complexes from simulations of EPR and Mdssbauer spectra; in the case of the tetrakis(2, 4, 6-trimethoxyphenyl)porphyrin complex, the parameters have been derived from EPR simulations alone because of difficulties in obtaining good-quality Mdssbauer data. D is similar in magnitude for all three complexes, while 7° exhibits magneto-structural variations. Nonzero values for J^d indicate a small anisotropy in the coupling of all three complexes. The resonance Raman spectra of the high-frequency region show that the marker bands v₂, v₁₁, and v₄ of all three complexes behave as expected for formation of π porphyrin radicals, supporting the assignment of the oxoferryl porphyrin π cation radical structure to the oxidized species.