Redox cycling in the activation of peroxides by iron porphyrin and manganese complexes. ‘Catching’ catalytic active intermediates

• Generation and reactivity of Compound I and II models under aqueous conditions.
• Iron porphyrin models for Compounds 0, I, and II in P450 model oxygenation reactions.
• Experimental and theoretical studies as a source of mechanistic information on the reactivity of heme enzyme mimics.
• Manganese complexes as catalysts for the oxidative degradation of organic dyes.

Understanding the redox cycling of metal ions in natural and biomimetic systems for dioxygen activation in catalytic oxidation processes at the molecular level has stood at the center of interest for many years, both from fundamental and applied perspectives. In this review, kinetic and mechanistic studies on peroxide activation by iron porphyrin models of heme enzymes, as well as by manganese complexes, are reported. Valuable information on the mechanistic details of dioxygen activation and oxygen atom transfer reactions by cytochrome P450 obtained from biomimetic studies with the application of model heme complexes is presented. Detailed mechanistic insight into particular steps of the catalytic cycle of enzyme model compounds was obtained through the application of ambient or low temperature rapid scan and high pressure techniques, supported by computational studies. Efforts undertaken to find reaction conditions and appropriate synthetic porphyrin models that allow the generation and significant stabilization of the mimics of intermediates responsible for oxygen transfer in the catalytic cycle of cytochrome P450 or peroxidases, which reflect reactivities comparable to that observed in native enzymes, are described. The review covers studies on peroxide activation not only by iron(III) porphyrin complexes for the oxidation of organic compounds, but also by simple manganese(II) and manganese(III/IV) complexes capable of conducting efficient organic dyes degradation. Throughout this report, redox cycling of the central metal ion plays an important role and controls the pathway of the oxidation processes.

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