Mechanistic study demonstrates iron(IV) oxido generation via heterolytic cleavage in iron complexes, indicating viable pathways to avoid nonselective reactive oxygen species.
High Resolution Image Download MS PowerPoint Slide High-valent Fe(IV) oxido species are important intermediates in the catalyzed oxidation of organic compounds by nonheme iron enzymes. These species can be generated in biomimetic model complexes directly using oxygen atom transfer oxidants, e.g., PhIO and ClO – . Their formation by heterolysis of the O–O bond of putative Fe(II)-OOH species (formed from Fe(II) precursors and H 2 O 2 ) has scarcely been observed. Reaction with near-stoichiometric H 2 O 2 typically shows initial formation of Fe(III)-OH and Fe(III)-OOH species, with homolytic O–O bond cleavage thereafter proposed to generate the Fe(IV)═O state. Here, we show that [(N4Py)Fe(IV)═O] 2+ (where N4Py = 1,1-di(pyridin-2-yl)- N,N -bis(pyridin-2-ylmethyl)methanamine) is formed with substoichiometric H 2 O 2 in methanol through heterolytic cleavage of the O–O bond of an Fe(II)-OOH intermediate. Temperature-dependent studies show that the ligand exchange reactions preceding formation of the Fe(II)-OOH species and subsequent comproportionations limit the yield of the Fe(IV)═O species. Furthermore, comproportionation proceeds through hydrogen atom transfer from [(N4Py)Fe(II)(OH 2 )] 2+ to [(N4Py)Fe(IV)═O] 2+ . These data rationalize the extent of the initial conversion of [(N4Py)Fe(II)(CH 3 CN)] 2+ to [(N4Py)Fe(IV)═O] 2+ under conditions relevant to catalytic oxidations. The heterolytic pathway to formation of [(N4Py)Fe(IV)═O] 2+ is a key step in the development of iron(II) oxidation catalysts that can cycle between the Fe(II) and Fe(IV)═O states, avoiding nonselective reactive oxygen species.
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Chen et al. (2025) studied this question.
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