Nature has demonstrated the ability to functionalize strong substrate C–H bonds with enzymes that have heme or nonheme iron active sites. Formally oxoiron(V) species are potentially involved in such chemistry in the action of cytochrome P450, soluble methane monooxygenase (sMMO), and Rieske oxygenases. Our recent biomimetic efforts have focused on accumulating evidence that such high-valent species can be generated in nonheme ligand environments in the reactions of bio-inspired nonheme iron catalysts with H2O2 or peracids. Mass spectrometric evidence for (N4)FeV(O)(OH) oxidants has been obtained in several cases, but experimental insight into the electronic structure of this elusive species could be obtained only more recently. This talk will focus on two aspects of Fe(V)=O chemistry: a) the activation of (N4 or N5)Fe(III)–OOH intermediates to form highly reactive Fe(V)=O oxidants that can hydroxylate cyclohexane and benzene within seconds at -40 °C and b) the spectroscopic characterization of an (N4)Fe(V)=O oxidant from the reaction of its iron precursor and peracid at -40 °C that exhibits the fastest rate for cyclohexane hydroxylation determined to date for a nonheme iron center. Based on various spectroscopic results, this species is concluded to possess a unique electronic structure that is predominantly FeV(O)(O2CR) in character but mixed in with contributions from its FeIII(OOC(O)R) and FeIV(O)(carboxyl radical) electromers.

Functionalizing strong C–H bonds with nonheme FeV=O oxidants, seen and unseen

2019 Fall National Meeting

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