Factors That Affect the Nature of the Final Oxidation Products in 'Peroxo-Shunt' Reactions of Iron–Porphyrin Complexes

摘要

The present study focuses onthe oxidation of the water-soluble andwater-insoluble iron(III)—porphyrincomplexes [FeIII(TMPS)] and [Fem-(TMP)] (TMPS =meso-tetrakis(2,4,6-trimethyl-3-sulfonatophenyl)porphyri- nato, TMP=meso-tetrakis(2,4,6-trime-thylphenyl)porphyrinato), respectively,by meta-chloroperoxybenzoic acid (m-CPBA) in aqueous methanol and aque-ous acetonitrile solutions of varyingacidity. With the application of a low-temperature rapid-scan UV/Vis spec-troscopic technique, the complete spec-tral changes that accompany the forma-tion and decomposition of the primaryproduct of 0-0 bond cleavage in the acylperoxoiron(III)—porphyrin inter-mediate [(P)Fem-00X] (P=porphy-rin) were successfully recorded andcharacterized. The results clearly indi-cate that the 0-0 bond in m-CPBA isheterolytically cleaved by the studiediron(III)—porphyrin complexes inde-pendent of the acidity of the reactionmedium. The existence of two differentoxidation products under acidic andbasic conditions is suggested not to bethe result of a mechanistic changeoverin the mode of 0-0 bond cleavage ongoing from low to high pH values, butrather the effect of environmentalchanges on the actual product of the0-0 bond cleavage in [(P)Fe111—00X] . The oxoiron(IV)—porphyrincation radical formed as a primary oxi-dation product over the entire pHrange can undergo a one- or two-elec-tron reduction depending on the select-ed reaction conditions. The presentstudy provides valuable information forthe interpretation and improved under-standing of results obtained in product-analysis experiments.