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Factors That Affect the Nature of the Final Oxidation Products in “Peroxo‐Shunt” Reactions of Iron–Porphyrin Complexes
Author(s) -
Franke Alicja,
Wolak Maria,
van Eldik Rudi
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200900453
Subject(s) - porphyrin , aqueous solution , chemistry , bond cleavage , photochemistry , acetonitrile , methanol , radical ion , medicinal chemistry , inorganic chemistry , catalysis , organic chemistry , ion
Abstract The present study focuses on the oxidation of the water‐soluble and water‐insoluble iron(III)–porphyrin complexes [Fe III (TMPS)] and [Fe III (TMP)] (TMPS= meso ‐tetrakis(2,4,6‐trimethyl‐3‐sulfonatophenyl)porphyrinato, TMP= meso ‐tetrakis(2,4,6‐trimethylphenyl)porphyrinato), respectively, by meta ‐chloroperoxybenzoic acid ( m ‐CPBA) in aqueous methanol and aqueous acetonitrile solutions of varying acidity. With the application of a low‐temperature rapid‐scan UV/Vis spectroscopic technique, the complete spectral changes that accompany the formation and decomposition of the primary product of OO bond cleavage in the acylperoxoiron(III)–porphyrin intermediate [(P)Fe III OOX] (P=porphyrin) were successfully recorded and characterized. The results clearly indicate that the OO bond in m ‐CPBA is heterolytically cleaved by the studied iron(III)–porphyrin complexes independent of the acidity of the reaction medium. The existence of two different oxidation products under acidic and basic conditions is suggested not to be the result of a mechanistic changeover in the mode of OO bond cleavage on going from low to high pH values, but rather the effect of environmental changes on the actual product of the OO bond cleavage in [(P)Fe III OOX]. The oxoiron(IV)–porphyrin cation radical formed as a primary oxidation product over the entire pH range can undergo a one‐ or two‐electron reduction depending on the selected reaction conditions. The present study provides valuable information for the interpretation and improved understanding of results obtained in product‐analysis experiments.