Generation of [(N4Py)Fe(IV)═O]²⁺ through Heterolytic O-O Bond Cleavage in [(N4Py)Fe(II)(OOH)]

Area of Science:

• Bioinorganic Chemistry
• Catalysis
• Oxidation Chemistry

Background:

• High-valent Fe(IV) oxido species are crucial intermediates in nonheme iron enzyme-catalyzed oxidations.
• Biomimetic models typically generate these species using oxygen atom transfer oxidants, with heterolytic O-O bond cleavage of Fe(II)-OOH intermediates being rarely observed.
• Conventional reactions with H₂O₂ often lead to Fe(III)-OH/OOH and subsequent homolytic O-O bond cleavage.

Purpose of the Study:

• To investigate the formation of high-valent Fe(IV) oxido species via heterolytic O-O bond cleavage of an Fe(II)-OOH intermediate.
• To elucidate the factors limiting the yield of the Fe(IV)═O species in biomimetic iron complexes.
• To understand the reaction mechanism and rationalize the conversion efficiency under catalytic conditions.

Main Methods:

• Synthesis and characterization of the [(N4Py)Fe(IV)═O]²⁺ complex.
• Reaction of the iron complex with substoichiometric amounts of hydrogen peroxide (H₂O₂) in methanol.
• Temperature-dependent kinetic studies to analyze ligand exchange and comproportionation reactions.

Main Results:

• The [(N4Py)Fe(IV)═O]²⁺ species was successfully formed through heterolytic cleavage of the O-O bond in an Fe(II)-OOH intermediate using substoichiometric H₂O₂.
• Ligand exchange and comproportionation reactions were identified as key factors limiting the yield of the Fe(IV)═O species.
• Comproportionation was shown to proceed via hydrogen atom transfer from [(N4Py)Fe(II)(OH₂)]²⁺ to [(N4Py)Fe(IV)═O]²⁺.

Conclusions:

• The heterolytic pathway for Fe(IV)═O formation from Fe(II)-OOH intermediates is viable and significant under specific conditions (substoichiometric H₂O₂).
• Understanding these mechanistic details provides insights into the reactivity of nonheme iron complexes and guides the development of efficient iron(II) oxidation catalysts.
• This pathway offers a route to selective iron-catalyzed oxidations by avoiding the generation of less selective reactive oxygen species.