Abstract
The modeling of iron porphyrins is essential in the study of heme proteins. These complexes readily undergo autooxidation and dimerization; however, this dimerization process can be inhibited by introducing phenyl groups. Herein, the dimerization of highly substituted iron(III) porphyrins is investigated. The stability of water-insoluble iron(III) hydroxo complexes was monitored via thin-layer chromatography and was found to increase with the number of phenyl groups. Dodecaphenyl-substituted complexes formed hydroxo complexes, tetraphenyl and hexaphenyl complexes formed [Formula: see text]-oxo dimers, and octaphenyl and decaphenyl complexes existed as hydroxo complex-[Formula: see text]-oxo dimer mixtures. Crystals of the dodecaphenyl-substituted iron(III) hydroxo complexes were successfully isolated. The decaphenyl-substituted complex was unique in that the respective crystals of both the hydroxo complexes and [Formula: see text]-oxo dimer could be isolated from the chloride complexes. Furthermore, the synthesis and proton equilibria of the new porphyrin iron(III) water-soluble complexes were investigated. Under neutral to basic conditions, at equilibrium, dodecaphenyl-substituted complexes exclusively formed hydroxo complexes, whereas octaphenyl, hexaphenyl, and tetraphenyl complexes exclusively formed [Formula: see text]-oxo dimers, and decaphenyl complexes existed as hydroxo complex-[Formula: see text]-oxo dimer mixtures. Additionally, the order of the dimerization reaction was examined using the initial-rate and half-life methods, which confirmed that the dimerization is a second-order reaction that follows a mechanism wherein two hydroxo complexes form a dihydroxo-bridged intermediate. This result was supported by the dimerization of water-soluble iron(III) hydroxo complexes. The new hydroxo complexes with non-planar porphyrin cores synthesized in this study are expected to have a significant impact on heme protein reaction modeling.
Published Version
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