High-valent nonheme iron complexe

Oxidation Cataiysis with High-Valent Nonheme Iron Complexes... 

As for the formation of high-valent oxo species of nonheme iron complexes, Lange et al. reported about evidence for a nonheme Fe(IV)=0 species. No direct spectroscopic evidence for the species has been obtained, but the intramolecular hydroxylation of a ligand phenyl moiety was explained by its involvement in the mechanism. This supports the hypothesis that Fe(IV)=0 species can be the active species responsible for substrate oxidation in the class of oxygen-activating nonheme iron enzymes. Wada et al. have isolated and characterized... 

The transient nature of spectroscopically detected reaction intermediates in the reaction cycle of nonheme di-iron enzymes makes it difficult to obtain detailed structural information. Characterization of biomimetic 62-adducts derived from synthetic systems facilitates our understanding of the electronic and geometric structures of their biological counterparts. Within synthetic platforms, (peroxo)di-iron(III) species can be accessed either by oxygenation of mono- or di-iron(II) complexes or by reaction of di-iron(III) complexes with hydrogen peroxide. Formation of high-valent iron(III)iron(IV) species proceeds either via biomimetic one-electron reduction of the (peroxo)di-iron(III) core or by one-electron chemical oxidation of a di-iron(III) precursor. Decomposition of an alkylperoxoiron(III) adduct can afford a di-iron(IV) species. 

High-valent iron(IV)-oxo complexes of heme and nonheme ligands in oxygenation reactions 07ACR522. 

We have explored the reactivity of Fe(TPA) complexes with peroxides and found that such centers are capable of activating peroxides to functionalize alkanes in a catalytic fashion. Because of the efficient stoichiometric transfer of coordinated halide onto the alkane substrate, we have been able to deduce the participation of an [(TPA)Fe(X)=0] + species in these reactions. Finally the high valent intermediate can be stabilized under appropriate conditions to allow its spectroscopic characterization. These experiments provide significant insight into how nonheme iron centers may function in enzyme active sites for the functionalization of unactivated C-H bonds. 

The high-valent iron-oxo sites of nonheme iron enzymes catalyze a variety of reactions (halogenation and hydroxylation of alkanes, desaturation and cyclization, electrophilic aromatic substitution, and cis-dihydroxylation of olefins) [lb]. Most of these (and other) reactions have also been achieved and studied with model systems [Ic, 2a-c]. With the bispidine complexes, we have primarily concentrated on olefin epoxidation and dihydroxylation, alkane hydroxylation and halogenation, and sulfoxidation and demethylation processes. The focus in these studies so far has been on a thorough analysis of the reaction mechanisms rather than the substrate scope and catalyst optimization. 

---