A Pseudotetrahedral Terminal Oxoiron(IV) Complex: Mechanistic Promiscuity in C−H Bond Oxidation Reactions

Abstract

S=2 oxoiron(IV) species act as reactive intermediates in the catalytic cycle of nonheme iron oxygenases. The few available synthetic S=2 FeIV=O complexes known to date are often limited to trigonal bipyramidal and very rarely to octahedral geometries. Herein we describe the generation and characterization of an S=2 pseudotetrahedral FeIV=O complex 2 supported by the sterically demanding 1,4,7‐tri‐tert‐butyl‐1,4,7‐triazacyclononane ligand. Complex 2 is a very potent oxidant in hydrogen atom abstraction (HAA) reactions with large non‐classical deuterium kinetic isotope effects, suggesting hydrogen tunneling contributions. For sterically encumbered substrates, direct HAA is impeded and an alternative oxidative asynchronous proton‐coupled electron transfer mechanism prevails, which is unique within the nonheme oxoiron community. The high reactivity and the similar spectroscopic parameters make 2 one of the best electronic and functional models for a biological oxoiron(IV) intermediate of taurine dioxygenase (TauD‐J).

Entropic influence on the generation of Fe(iv)O species at mononuclear Fe(ii) sites in metal–organic frameworks

“…[28][29][30][31][32] Solid-state Fe(IV)O systems have been also investigated for their potential to store methane in the case of MOF74, 33 NO adsorption in Al-rich beta zeolites 34 and in MOFs, 35 NO and N 2 O reduction by NH 3 within the framework of the zeolite Fe-BEA, [36][37][38] and the decomposition of nitrous oxide (N 2 O) in the zeolites Fe-FER, Fe-BEA, and Fe-MFI. 39,40 Whereas much is known about the generation and reactivity of Fe(IV)oxo in biochemistry, biomimetic chemistry and solution chemistry, [41][42][43][44][45][46][47] the study of these species supported by inorganic crystalline materials is still in its infancy. In particular, the generation of a ferryl group in the solid state and its regeneration as this species is consumed during a catalytic oxidation process, remain to be addressed.…”

“…Whereas much is known about the generation and reactivity of Fe( iv )oxo in biochemistry, biomimetic chemistry and solution chemistry, 41–47 the study of these species supported by inorganic crystalline materials is still in its infancy. In particular, the generation of a ferryl group in the solid state and its regeneration as this species is consumed during a catalytic oxidation process, remain to be addressed.…”

Catalytic properties of the ferryl ion in the solid state: a computational review

“…To date, the vast majority of the studies on Fe(IV)O systems have focused on gas phase or solvated systems, with a recent emphasis on high-spin complexes, [24][25][26][27][28][29][30] whereas far less is known about their catalytic activity in the solid state. A limited number of theoretical studies have been published very recently to investigate, e.g., the oxidation of methane and ethane 10,[31][32][33][34][35][36][37][38][39] in metal-organic frameworks (MOFs), of benzene on graphene, 40 of CO with N 2 O through an oriented external electric field in the MOF Fe 3 (btc) 2 41 and of methane [42][43][44][45][46][47][48] and propane 49 in zeolites.…”

“…To date, the vast majority of the studies on Fe( iv )O systems have focused on gas phase or solvated systems, with a recent emphasis on high-spin complexes, 24–30 whereas far less is known about their catalytic activity in the solid state. A limited number of theoretical studies have been published very recently to investigate, e.g.…”