An Iron(III)-Oxyl Complex and Redox Tautomerization to its Iron(IV)-Oxo Form in Gas Phase

Le résumé fourni par la source

Despite the central role proposed for iron(III)-oxyl (Fe III -O•) species in enzymatic and synthetic C-H bond oxidation reactions, such intermediates have eluded direct experimental characterization. We now report the spectroscopic and theoretical characterizations of an Fe III -O• moiety supported by a redox-active bbpya (Hbbpya = N,N-bis(2,2ʹ-bipyrid-6yl) amine) ligand. Iodosobenzene oxidation of the iron(II) complex in acetonitrile (MeCN) yields [(bbpya)Fe III -O•]+ , which has an electronically equivalent structure of the Fe IV =O species. The oxidation state of the iron center in MeCN was shown to be +3 based on Mössbauer spectroscopy; the Fe-O stretching mode was observed at 762 cm −1 in the resonance Raman spectrum and the Fe-O bond length was determined to be 1.75 Å by X-ray absorption spectroscopy (XAS). We could also isolate the oxoiron moiety in the gas phase and confirm a redox tautomerization to [(bbpya)Fe IV =O)] + by infrared photodissociation (IRPD) and XAS methods. Notably, the Fe-O stretching frequency is now shifted to higher energy at 863 cm -1 , consistent with an Fe-O double bond. An Fe L3 excitation energy of 709.2 eV further confirms the presence of an Fe(IV) oxidation state in the gas phase. The stabilization of Fe III -O• and Fe IV =O forms in solution and gas phases, respectively, are attributed to the differences in the intermolecular interactions in the two phases. [(bbpya)Fe III -O•] + is able to perform oxygen atom transfer (OAT) and hydrogen atom abstraction (HAA) reactions with impressive rate constants, which corroborate the plausible role of Fe III -O• in biological oxidation reactions.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.