+++ High-valent iron (IV)–oxo complexes of heme and non-heme ligands in oxygenation reactions.pdf

High-Valent Iron(IV)–Oxo Complexes of Heme and Non-Heme Ligands in Oxygenation Reactions WONWOO NAM* Department of Chemistry, Division of Nano Sciences, and Center for Biomimetic Systems, Ewha Womans University, Seoul 120-750, Korea Received February 7, 2007 ABSTRACT High-valent iron(IV)–oxo species have been implicated as the key reactive intermediates in the catalytic cycles of dioxygen activation by heme and non-heme iron enzymes. Our understanding of the enzymatic reactions has improved greatly via investigation of spectroscopic and chemical properties of heme and non-heme iron(IV)–oxo complexes. In this Account, reactivities of synthetic iron(IV)–oxo porphyrin π-cation radicals and mononuclear non- heme iron(IV)–oxo complexes in oxygenation reactions have been discussed as chemical models of cytochrome P450 and non-heme iron enzymes. These results demonstrate how mechanistic devel- opments in biomimetic research can help our understanding of dioxygen activation and oxygen atom transfer reactions in nature. 1. Introduction Heme and non-heme iron enzymes catalyze a diverse array of important metabolic transformations that require the binding and activation of dioxygen.1–5 Our under- standing of the catalytic reactions of the enzymes, espe- cially the nature of active oxidizing species, has improved recently with the intensive mechanistic studies of the enzymes and their model compounds. One example is the fact that a catalytic cycle of dioxygen activation and oxygen atom transfer by cytochrome P450 enzymes (CYP 450) has been proposed (Figure 1a), and high-valent iron(IV)–oxo porphyrin π-cation radicals, termed com- pound I and two oxidizing equivalents above the resting ferric state (see the structure in Figure 1a), are believed to transfer their oxygen atom to organic substrates. Very recently, a high-valent iron(IV)–oxo porphyrin π-cation radical has been characterized in CYP 450, but its detailed physical and chemical properties remained elusive in future stud