Radical Intermediates in Monooxygenase Reactions of Rieske Dioxygenases

Chakrabarty, S.; Austin, Rachel N.; Deng, Dayi; Groves, John T.; Lipscomb, John D.

doi:10.1021/ja068188v

Cited by 105 publications

(89 citation statements)

References 27 publications

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“…84). This is the first Fe VI coordination complex ever reported, with the ferrate anion FeO 4 2 − being the only other known example of an Fe VI ion. However, just like all previous nitridoiron species, complex [(Me 3 cy-ac)Fe VI (N)] 2 + is only stable in cryogenic matrices and decomposes to a high-spin Fe III species on warming.…”

Section: Iron-nitrido Model Complexesmentioning

confidence: 80%

“…Haem and non-haem proteins use these reactive intermediates to couple the activation of dioxygen to the oxidation of their substrates. In most cases, an oxygen atom is inserted into an unactivated C-H bond of the substrate; for example, in hydroxylation reactions [1][2][3][4][5][6][7][8][9][10] . However, many other reactions, including halogenation, desaturation, cyclization, epoxidation and decarboxylation, are also known to involve oxoiron species 1,3 .…”

mentioning

confidence: 99%

“…Accordingly, Tiago de Oliveira et al 32 reported the synthesis of an oxoiron(V) ( An Fe V (O)(OH) species has been implicated as the active oxidant responsible for the cis-dihydroxylation of C = C double bonds 2,4,33 and the oxidation of water 34 in a number of ironcontaining non-haem natural and model systems, but with only indirect proof of its existence [35][36][37] . However, the spectroscopically characterized [(TAML)Fe V (O)] − anion, which is the only known isolable oxoiron(V) species in the literature, was found to be a sluggish oxidant 32 38 .…”

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confidence: 99%

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The biology and chemistry of high-valent iron–oxo and iron–nitrido complexes

2012

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selective functionalization of unactivated c-H bonds and ammonia production are extremely important industrial processes. a range of metalloenyzmes achieve these challenging tasks in biology by activating dioxygen and dinitrogen using cheap and abundant transition metals, such as iron, copper and manganese. High-valent iron-oxo and -nitrido complexes act as active intermediates in many of these processes. the generation of well-described model compounds can provide vital insights into the mechanism of such enzymatic reactions. advances in the chemistry of model high-valent iron-oxo and -nitrido systems can be related to our understanding of the biological systems.H igh-valent oxoiron(IV) and formally oxoiron(V) species have been spectroscopically identified as active intermediates in the catalytic cycles of a number of enzymatic systems 1-10 . Haem and non-haem proteins use these reactive intermediates to couple the activation of dioxygen to the oxidation of their substrates. In most cases, an oxygen atom is inserted into an unactivated C-H bond of the substrate; for example, in hydroxylation reactions [1][2][3][4][5][6][7][8][9][10] . However, many other reactions, including halogenation, desaturation, cyclization, epoxidation and decarboxylation, are also known to involve oxoiron species 1,3 . Superoxidized iron complexes with (valence) isoelectronic imido and nitrido ligands, as well as 'surface nitrides' , have also been implicated as key intermediates in the nitrogen atom transfer reactions 11 , the biological synthesis of ammonia by the nitrogenase enzyme 12-16 and the industrial Haber-Bosch process 17 .The generation of well-described model compounds can provide vital insights into the mechanism of such enzymatic reactions. Consequently, considerable effort has been made by synthetic chemists to prepare viable models for the putative reaction intermediates in the catalytic cycles of O 2 and N 2 activating enzymes. In this review, we provide an overview of all high-valent oxoiron and nitridoiron species that have been either identified or proposed as reactive intermediates in biology. Subsequently, we summarize some of the recent advances in bioinorganic chemistry that have led to the identification and isolation of iron complexes in unusually high formal oxidation states, containing iron-oxygen or iron-nitrogen multiple bonds. The spectroscopic characterization and the reactivity studies of these model complexes provide vital insights into the mechanism that nature uses to induce the reductive cleavage of dioxygen or dinitrogen in carrying out a number of important biochemical oxidative transformations. Moreover, the comparative review of the electronic structures of the isoelectronic oxoiron and nitridoiron functionalities reveals that the Fe-N bonds are intrinsically more covalent than the Fe-O bonds.

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Section: Iron-nitrido Model Complexesmentioning

confidence: 80%

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The biology and chemistry of high-valent iron–oxo and iron–nitrido complexes

2012

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“…[45] On the other hand, the high-spin (S = 5/2) Fe III ─OOH intermediate, proposed to be formed in Rieske dioxygenases (RDO), [157,158,159] should have oxidant ability in electrophilic aromatic substitution reactions (note that alternative intermediates in RDO were also proposed [160,161] Figure 2) was crystallographically defined only as late as in 2014. [165] This synthetic system was shown to undergo both an aliphatic C─H activation and nucleophilic oxidation reaction.…”

Section: Mononuclear Ferric-hydroperoxo Active Site: C─h + Hoo─fe IIImentioning

confidence: 99%

Mono- and binuclear non-heme iron chemistry from a theoretical perspective

et al. 2016

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In this minireview, we provide an account of the current state-of-the-art developments in the area of mono-and binuclear non-heme enzymes (NHFe and NHFe2) and the smaller NHFe(2) synthetic models, mostly from a theoretical and computational perspective. The sheer complexity, and at the same time the beauty, of the NHFe(2) world represent a challenge for both experimental as well as theoretical methods. We emphasize that the concerted progress on both theoretical and experimental side is a conditio sine qua non for future understanding, exploration and utilization of the NHFe(2) systems.After briefly discussing the current challenges and advances in the computational methodology, we review the recent spectroscopic and computational studies of NHFe(2) enzymatic and inorganic systems and highlight the correlations between various experimental data (spectroscopic, kinetic, thermodynamic, electrochemical) and computations. Throughout, we attempt to keep in mind the most fascinating and attractive phenomenon in the NHFe(2) chemistry which is the fact that despite the strong oxidative power of many reactive intermediates, the NHFe(2) enzymes perform catalysis with high selectivity. We conclude with our personal viewpoint and hope that further developments in quantum chemistry and especially in the field of multireference wave function methods are needed to have a solid theoretical basis for the NHFe(2) studies, mostly by providing benchmarking and calibration of the computationally efficient and easy-to-use DFT methods.

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“…60,61 In first place isotopic analysis shows that hydrogen peroxide is the exclusive source of oxygen atoms that end up in the epoxide (Scheme 3c), discarding water and atmospheric O 2 as alternative sources. Indeed, reactions with O2 as the sole oxidant do not produce the epoxide.…”

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Iron Catalyzed Highly Enantioselective Epoxidation of Cyclic Aliphatic Enones with Aqueous H₂O₂

et al. 2016

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An iron complex with a C 1 -symmetric tetradentate N-based ligand catalyze the asymmetric epoxidation of cyclic enones and cyclohexene ketones with aqueous hydrogen peroxide, providing the corresponding epoxides in good to excellent yields and enantioselectivities (up to 99 % yield, and 95 % ee), under mild conditions and in short reaction times. Evidence is provided that reactions involve an electrophilic oxidant, and this element is employed in performing site selective epoxidation of enones containing two alkene sites.Introduction. Asymmetric epoxidation is a valuable reaction because chiral epoxides are versatile building blocks in synthetic organic chemistry. 1-4 Catalytic epoxidation methodologies based on iron complexes and peroxides (especially H 2 O 2 ), which can be considered as biologically inspired, are interesting because of the availability and low environmental impact of these reagents. [5][6][7][8][9][10][11][12][13][14][15]16 Despite appealing, the approach is challenging because it requires the design of iron coordination complexes that can activate the O-O bond of peroxides to create selective metal based oxidants, and avoid the often facile production of hydroxyl radicals via the Fenton reaction. 10,11,17,18 Recent reports have disclosed successful examples where asymmetric epoxidation is accomplished, in some cases producing high levels of stereoselectivity ( Figure 1). [19][20][21][22][23][24][25][26][27] Highly enantioselective epoxidation of difficult substrates such as ,-disubstituted aromatic enones and -alkyl styrenes, not accessible by other methods, have also been described. 23,24 However, a major limitation still resides at the fact that iron catalyzed asymmetric epoxidations have been limited in scope to olefins conjugated to aromatic rings, [19][20][21][22]23,[24][25][26][27][28][29][30][31][32][33][34][35] and remains to be accomplished for aliphatic substrates. Particularly interesting are cyclic aliphatic enones. Cyclic -epoxide enones are structures found in a number of natural products, 36 and are also valuable synthons that can be further elaborated into precious building blocks for organic synthesis. 37 However, their asymmetric epoxidation is notoriously difficult. Modest to good enantioselectivities have been obtained with chiral hydroperoxides, 38,39 poly(aminoacids) catalysts, 40 ammonium salt catalysts, [41][42][43] and metal based catalysts 21,22,44,45 , but excellent enantioselectivities have only been described by List and co-workers using cinchona alkaloid derived organocatalysts and hydrogen peroxide as oxidant. The main drawbacks of this system are the requirement of relatively high catalyst loadings (up to 10 %) and long reaction times (from 24 to 168 h). In addition,  and ' substituted enones are not valid substrates for the system. Highly enantioselective epoxidations that could improve these aspects will

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Radical Intermediates in Monooxygenase Reactions of Rieske Dioxygenases

Cited by 105 publications

References 27 publications

The biology and chemistry of high-valent iron–oxo and iron–nitrido complexes

The biology and chemistry of high-valent iron–oxo and iron–nitrido complexes

Mono- and binuclear non-heme iron chemistry from a theoretical perspective

Iron Catalyzed Highly Enantioselective Epoxidation of Cyclic Aliphatic Enones with Aqueous H₂O₂

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Radical Intermediates in Monooxygenase Reactions of Rieske Dioxygenases

Cited by 105 publications

References 27 publications

The biology and chemistry of high-valent iron–oxo and iron–nitrido complexes

The biology and chemistry of high-valent iron–oxo and iron–nitrido complexes

Mono- and binuclear non-heme iron chemistry from a theoretical perspective

Iron Catalyzed Highly Enantioselective Epoxidation of Cyclic Aliphatic Enones with Aqueous H2O2

Contact Info

Product

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Iron Catalyzed Highly Enantioselective Epoxidation of Cyclic Aliphatic Enones with Aqueous H₂O₂