Identification and Spectroscopic Characterization of Nonheme Iron(III) Hypochlorite Intermediates

Draksharapu, Apparao; Angelone, Davide; Quesne, Matthew G.; Padamati, Sandeep K.; Gómez, Laura; Hage, Ronald; Costas, Miguel; Browne, Wesley R.; Visser, Sam P. de

doi:10.1002/anie.201411995

Cited by 37 publications

(35 citation statements)

References 40 publications

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“…In no case did we find products incorporating chlorine or acetate moieties, demonstrating that the NaOCl/AcOH oxidant is not responsible for the substrate oxidation. 32,33 …”

Section: Resultsmentioning

confidence: 99%

Tuning the Reactivity of Terminal Nickel(III)–Oxygen Adducts for C–H Bond Activation

et al. 2016

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Two metastable NiIII complexes, [NiIII(OAc)(L)] and [NiIII(ONO2)(L)] (L = N,N’-(2,6-dimethylphenyl)-2,6-pyridinedicarboxamidate, OAc = acetate), were prepared, adding to the previously prepared [NiIII(OCO2H)(L)], with the purpose of probing the properties of terminal late-transition metal oxidants. These high-valent oxidants were prepared by the one-electron oxidation of their NiII precursors ([NiII(OAc)(L)]h− and [NiII(ONO2)(L)]−) with tris(4-bromophenyl)ammoniumyl hexachloroantimonate. Fascinatingly, the reaction between any [NiII(X)(L)]− and NaOCl/acetic acid (AcOH) or cerium ammonium nitrate ((NH4)2[CeIV(NO3)6], CAN), yielded [NiIII(OAc)(L)] and [NiIII(ONO2)(L)], respectively. An array of spectroscopic characterizations (electronic absorption, electron paramagnetic resonance, X-ray absorption spectroscopies), electrochemical methods, and computational predictions (density functional theory) have been used to determine the structural, electronic, and magnetic properties of these highly reactive metastable oxidants. The NiIII-oxidants proved competent in the oxidation of phenols (weak O–H bonds) and a series of hydrocarbon substrates (some with strong C–H bonds). Kinetic investigation of the reactions with di-tert-butylphenols showed a 15-fold enhanced reaction rate for [NiIII(ONO2)(L)] compared to [NiIII(OCO2H)(L)] and [NiIII(OAc)(L)], demonstrating the effect of electron-deficiency of the O-ligand on oxidizing power. The oxidation of a series of hydrocarbons by [NiIII(OAc)(L)] was further examined. A linear correlation between the rate constant and the BDE of the C–H bonds in the substrates was indicative of a hydrogen atom transfer mechanism. The reaction rate with DHA (k2 = 8.1 M−1s−1) compared favorably with the most reactive high-valent metal-oxidants, and showcases the exceptional reactivity of late transition metal-oxygen adducts.

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“…In no case did we find products incorporating chlorine or acetate moieties, demonstrating that the NaOCl/AcOH oxidant is not responsible for the substrate oxidation. 32,33 …”

Section: Resultsmentioning

confidence: 99%

Tuning the Reactivity of Terminal Nickel(III)–Oxygen Adducts for C–H Bond Activation

et al. 2016

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“…Currently, there are very few industrial applications of haloperoxidases, due to their low selectivity and stability. In addition, few biomimetic models of halogenases and haloperoxidases have been reported [65][66][67][68][69]. Cys 400 Figure 3.…”

Section: Classification Of Halogenasesmentioning

confidence: 99%

A Comparative Review on the Catalytic Mechanism of Nonheme Iron Hydroxylases and Halogenases

Timmins

Visser

2018

Catalysts

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Enzymatic halogenation and haloperoxidation are unusual processes in biology; however, a range of halogenases and haloperoxidases exist that are able to transfer an aliphatic or aromatic C–H bond into C–Cl/C–Br. Haloperoxidases utilize hydrogen peroxide, and in a reaction with halides (Cl−/Br−), they react to form hypohalides (OCl−/OBr−) that subsequently react with substrate by halide transfer. There are three types of haloperoxidases, namely the iron-heme, nonheme vanadium, and flavin-dependent haloperoxidases that are reviewed here. In addition, there are the nonheme iron halogenases that show structural and functional similarity to the nonheme iron hydroxylases and form an iron(IV)-oxo active species from a reaction of molecular oxygen with α-ketoglutarate on an iron(II) center. They subsequently transfer a halide (Cl−/Br−) to an aliphatic C–H bond. We review the mechanism and function of nonheme iron halogenases and hydroxylases and show recent computational modelling studies of our group on the hectochlorin biosynthesis enzyme and prolyl-4-hydroxylase as examples of nonheme iron halogenases and hydroxylases. These studies have established the catalytic mechanism of these enzymes and show the importance of substrate and oxidant positioning on the stereo-, chemo- and regioselectivity of the reaction that takes place.

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“…Our computational methods were calibrated and benchmarked previously and shown accurately to reproduce experimental resonance Raman spectra, infrared spectra as well as kinetic isotope effects and rate constants excellently. 21 , 22 We initially took the DFT optimized geometries of catalytic cycle intermediates with two oxygen atoms included from previous studies 12 and after reoptimizing with the methods described in the ESI † analyzed the absorption spectra for each species in the triplet and quintet spin states using various methods and basis sets. The focus of the calculations was on the iron( iii )–superoxo ( B ), iron( iii )-bicyclic ring-structure ( C ), iron( iv )–oxo–cysteinesulfoxide complex ( D and D′ ) as well as the iron( iii )–cysteine–sulfinic acid product complex ( E ).…”

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confidence: 99%

An iron–oxygen intermediate formed during the catalytic cycle of cysteine dioxygenase

et al. 2016

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Identification and Spectroscopic Characterization of Nonheme Iron(III) Hypochlorite Intermediates

Cited by 37 publications

References 40 publications

Tuning the Reactivity of Terminal Nickel(III)–Oxygen Adducts for C–H Bond Activation

Tuning the Reactivity of Terminal Nickel(III)–Oxygen Adducts for C–H Bond Activation

A Comparative Review on the Catalytic Mechanism of Nonheme Iron Hydroxylases and Halogenases

An iron–oxygen intermediate formed during the catalytic cycle of cysteine dioxygenase

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