MODELS FOR PEROXIDASE COMPOUND .1. GENERATION AND SPECTROSCOPIC CHARACTERIZATION OF NEW OXOFERRYL PORPHYRIN PI CATION RADICAL SPECIES

Oxoferryl porphyrin pi 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 pi cation radical complex generated from [tetramesitylporphyrinato]iron(III) triflate. The UV-vis and H-1 NMR spectra of the oxidized species are qualitatively similar. In the EPR, the complexes all show ferromagnetic coupling between ferryl and porphyrin pi cation radical spins yielding quartet states. However, the average effective g values of the x,y 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(o) and J(d)= has been derived for the tetramesityl- and tetrakis(2,6-dichlorophenyl)porphyrin complexes from simulations of EPR and Mossbauer 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 Mossbauer data. D is similar in magnitude for all three complexes, while J(o) 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 nu2, nu11, and nu4 of all three complexes behave as expected for formation of pi porphyrin radicals, supporting the assignment of the oxoferryl porphyrin pi cation radical structure to the oxidized species.