The biomimetic oxidation of dieldrin using polyhalogenated metalloporphyrins

Hino, Fumio; Dolphin, David

doi:10.1039/a809080g

Cited by 14 publications

(14 citation statements)

References 12 publications

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“…[42] Similarly, radical-derived rearrangements were produced from model systems which involve only Cpd I as an electrophilic oxidant. [43,44] Thus, while one cannot rule out the presence of another oxidant, in the absence of Cpd I, at this stage of the research, the balance seems to favor the TSR scenario with only Cpd I as a plausible mechanism of hydroxylation by P450. [3] Two DFT studies of ethane hydroxylation were performed by Yoshizawa et al [29,30] using a model Cpd I with MeS Ϫ as a proximal ligand.…”

Section: Background: Theoretical Calculations Of Alkane Hydroxylationmentioning

confidence: 95%

The “Rebound Controversy”: An Overview and Theoretical Modeling of the Rebound Step in C−H Hydroxylation by Cytochrome P450

et al. 2004

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C−H hydroxylation by the enzyme cytochrome P450 is one of Nature’s important and most ubiquitous processes. There is strong evidence that the mechanism proceeds by initial hydrogen abstraction, from the alkane, by the high‐valent iron−oxo species of the enzyme, followed by a rebound of the alkyl radical to form the ferric−alcohol product complex (the Groves “rebound” mechanism). Nevertheless, the “rebound” mechanism is still controversial due to the ultrashort radical lifetimes deduced from radical‐clock experiments. This review describes the main elements of the controversy and its updated resolution by theory, with an emphasis on the controversial rebound step. The theoretically derived model for alkane hydroxylation is found to involve two‐state reactivity (TSR). In TSR, radicals are produced on two different spin‐state surfaces, and thereafter they react differently; on the low‐spin surface, the rebound proceeds with no product rearrangement and the lifetime of the radicals is ultrashort (or zero), while on the high‐spin surface the barrier for rebound is substantial and the lifetime of the radical is sufficiently long that rearrangement may compete with product formation by rebound. A new valence‐bond model is developed to model the rebound barrier on the high‐spin surface and conceptualize its dependence on the nature of the alkyl radical. The possible intermediacy of carbocationic intermediates alongside radicals is discussed. It is shown that the TSR scenario provides a satisfactory rationale for the controversial findings in the field, and makes verifiable predictions. One of the predictions of TSR is that the ratio of unrearranged to rearranged products, [U/R], will be subject to an intrinsic isotope effect that is substrate‐dependent. This prediction and its possible verification by experiment are discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

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Section: Background: Theoretical Calculations Of Alkane Hydroxylationmentioning

confidence: 95%

The “Rebound Controversy”: An Overview and Theoretical Modeling of the Rebound Step in C−H Hydroxylation by Cytochrome P450

et al. 2004

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“…For example, dieldrin 5 is known to be metabolized to the intramolecularly bridged ketone 6 and Dolphin has recently demonstrated that this can be produced directly by a biomimetic oxidation of 5 mediated by a highly halogenated iron porphyrin (Scheme 15). 109 The alcohol 7 is also produced in vivo and in vitro but as yet no chemical or biochemical conditions have been found that will convert it into the ketone (6). The most plausible explanation for its formation appears to be cyclization of an initially formed radical to give a chlorine stabilized one that then recombines with the iron stabilized hydroxy radical.…”

Section: Hydrocarbon Hydroxylationmentioning

confidence: 99%

Oxidizing species in the mechanism of cytochrome P450

2002

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This review discusses the mechanisms of oxygen activation by cytochrome P450 enzymes, the possible catalytic roles of the various iron--oxygen species formed in the catalytic cycle, and progress in understanding the mechanisms of hydrocarbon hydroxylation, heteroatom oxidation, and olefin epoxidation. The focus of the review is on recent results, but earlier work is discussed as appropriate. The literature through to February 2002 is surveyed, and 175 referenced are cited.

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“…Ethylbenzene was oxidized to sec-phenyl ethyl alcohol by 2 b,c,e in about 80 % yield (entry 10); cumene was converted to acetophenone by 2 b,c in about 40 % yield (entry 11). Oxidation of 9,10-dihydroanthracene (DHA), xanthene, and fluorene by 2 b,c,e gave anthrone, xanthone, fluorenone, respectively, in 40-46 % yields (entries [12][13][14].…”

Section: Reactions Of B-halogenated Dioxoruthenium(vi) Porphyrin Compmentioning

confidence: 99%

Hydrocarbon Oxidation by β‐Halogenated Dioxoruthenium(VI) Porphyrin Complexes: Effect of Reduction Potential (Ru^VI/V) and CH Bond‐Dissociation Energy on Rate Constants

Che

Zhang

et al. 2005

Chemistry A European J

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beta-Halogenated dioxoruthenium(VI) porphyrin complexes [Ru(VI)(F(28)-tpp)O(2)] [F(28)-tpp=2,3,7,8,12,13, 17,18-octafluoro-5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato(2-)] and [Ru(VI)(beta-Br(8)-tmp)O(2)] [beta-Br(8)-tmp=2,3,7,8,12,13,17,18-octabromo-5,10,15,20- tetrakis(2,4,6-trimethylphenyl)porphyrinato(2-)] were prepared from reactions of [Ru(II)(por)(CO)] [por=porphyrinato(2-)] with m-chloroperoxybenzoic acid in CH(2)Cl(2). Reactions of [Ru(VI)(por)O(2)] with excess PPh(3) in CH(2)Cl(2) gave [Ru(II)(F(20)-tpp)(PPh(3))(2)] [F(20)-tpp=5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato(2-)] and [Ru(II)(F(28)-tpp)(PPh(3))(2)]. The structures of [Ru(II)(por)(CO)(H(2)O)] and [Ru(II)(por)(PPh(3))(2)] (por=F(20)-tpp, F(28)-tpp) were determined by X-ray crystallography, revealing the effect of beta-fluorination of the porphyrin ligand on the coordination of axial ligands to ruthenium atom. The X-ray crystal structure of [Ru(VI)(F(20)-tpp)O(2)] shows a Ru=O bond length of 1.718(3) A. Electrochemical reduction of [Ru(VI)(por)O(2)] (Ru(VI) to Ru(V)) is irreversible or quasi-reversible, with the E(p,c)(Ru(VI/V)) spanning -0.31 to -1.15 V versus Cp(2)Fe(+/0). Kinetic studies were performed for the reactions of various [Ru(VI)(por)O(2)], including [Ru(VI)(F(28)-tpp)O(2)] and [Ru(VI)(beta-Br(8)-tmp)O(2)], with para-substituted styrenes p-X-C(6)H(4)CH=CH(2) (X=H, F, Cl, Me, MeO), cis- and trans-beta-methylstyrene, cyclohexene, norbornene, ethylbenzene, cumene, 9,10-dihydroanthracene, xanthene, and fluorene. The second-order rate constants (k(2)) obtained for the hydrocarbon oxidations by [Ru(VI)(F(28)-tpp)O(2)] are up to 28-fold larger than by [Ru(VI)(F(20)-tpp)O(2)]. Dual-parameter Hammett correlation implies that the styrene oxidation by [Ru(VI)(F(28)-tpp)O(2)] should involve rate-limiting generation of a benzylic radical intermediate, and the spin delocalization effect is more important than the polar effect. The k(2) values for the oxidation of styrene and ethylbenzene by [Ru(VI)(por)O(2)] increase with E(p,c)(Ru(VI/V)), and there is a linear correlation between log k(2) and E(p,c)(Ru(VI/V)). The small slope (approximately 2 V(-1)) of the log k(2) versus E(p,c)(Ru(VI/V)) plot suggests that the extent of charge transfer is small in the rate-determining step of the hydrocarbon oxidations. The rate constants correlate well with the C-H bond dissociation energies, in favor of a hydrogen-atom abstraction mechanism.

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The biomimetic oxidation of dieldrin using polyhalogenated metalloporphyrins

Abstract: Biomimetic oxidation of dieldrin produces the same metabolites as generated in vivo, which suggest a 'radical oxygenrebound' mechanism.

Cited by 14 publications

References 12 publications

The “Rebound Controversy”: An Overview and Theoretical Modeling of the Rebound Step in C−H Hydroxylation by Cytochrome P450

The “Rebound Controversy”: An Overview and Theoretical Modeling of the Rebound Step in C−H Hydroxylation by Cytochrome P450

Oxidizing species in the mechanism of cytochrome P450

Hydrocarbon Oxidation by β‐Halogenated Dioxoruthenium(VI) Porphyrin Complexes: Effect of Reduction Potential (Ru^VI/V) and CH Bond‐Dissociation Energy on Rate Constants

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The biomimetic oxidation of dieldrin using polyhalogenated metalloporphyrins

Abstract: Biomimetic oxidation of dieldrin produces the same metabolites as generated in vivo, which suggest a 'radical oxygenrebound' mechanism.

Cited by 14 publications

References 12 publications

The “Rebound Controversy”: An Overview and Theoretical Modeling of the Rebound Step in C−H Hydroxylation by Cytochrome P450

The “Rebound Controversy”: An Overview and Theoretical Modeling of the Rebound Step in C−H Hydroxylation by Cytochrome P450

Oxidizing species in the mechanism of cytochrome P450

Hydrocarbon Oxidation by β‐Halogenated Dioxoruthenium(VI) Porphyrin Complexes: Effect of Reduction Potential (RuVI/V) and CH Bond‐Dissociation Energy on Rate Constants

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Hydrocarbon Oxidation by β‐Halogenated Dioxoruthenium(VI) Porphyrin Complexes: Effect of Reduction Potential (Ru^VI/V) and CH Bond‐Dissociation Energy on Rate Constants