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Title: Beyond ferryl-mediated hydroxylation: 40 years of the rebound mechanism and C–H activation

Journal Article · · JBIC Journal of Biological Inorganic Chemistry

Since our initial report in 1976, the oxygen rebound mechanism has become the consensus mechanistic feature for an expanding variety of enzymatic C–H functionalization reactions and small molecule biomimetic catalysts. For both the biotransformations and models, an initial hydrogen atom abstraction from the substrate (R–H) by high-valent iron-oxo species (Fen=O) generates a substrate radical and a reduced iron hydroxide, [Fen-1–OH ·R]. This caged radical pair then evolves on a complicated energy landscape through a number of reaction pathways, such as oxygen rebound to form R–OH, rebound to a non-oxygen atom affording R–X, electron transfer of the incipient radical to yield a carbocation, R+, desaturation to form olefins, and radical cage escape. These various flavors of the rebound process, often in competition with each other, give rise to the wide range of C–H functionalization reactions performed by iron-containing oxygenases. In this review, we first recount the history of radical rebound mechanisms, their general features, and key intermediates involved. We will discuss in detail the factors that affect the behavior of the initial caged radical pair and the lifetimes of the incipient substrate radicals. Several representative examples of enzymatic C–H transformations are selected to illustrate how the behaviors of the radical pair [Fen-1–OH ·R] determine the eventual reaction outcome. Finally, we discuss the powerful potential of “radical rebound” processes as a general paradigm for developing novel C–H functionalization reactions with synthetic, biomimetic catalysts. We envision that new chemistry will continue to arise by bridging enzymatic “radical rebound” with synthetic organic chemistry.

Research Organization:
Energy Frontier Research Centers (EFRC) (United States). Center for Catalytic Hydrocarbon Functionalization (CCHF)
Sponsoring Organization:
USDOE SC Office of Basic Energy Sciences (SC-22)
Grant/Contract Number:
SC0001298
OSTI ID:
1397173
Journal Information:
JBIC Journal of Biological Inorganic Chemistry, Journal Name: JBIC Journal of Biological Inorganic Chemistry Journal Issue: 2-3 Vol. 22; ISSN 0949-8257
Publisher:
SpringerCopyright Statement
Country of Publication:
United States
Language:
English

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  • Journal of the American Chemical Society, Vol. 134, Issue 9 https://doi.org/10.1021/ja211679v
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Fluorine Transfer to Alkyl Radicals
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  • Journal of the American Chemical Society, Vol. 134, Issue 9 https://doi.org/10.1021/ja211679v
journal February 2012
Merging Visible-Light Photocatalysis and Transition-Metal Catalysis in the Copper-Catalyzed Trifluoromethylation of Boronic Acids with CF 3 I journal May 2012
Detection and Kinetic Characterization of a Highly Reactive Heme–Thiolate Peroxygenase Compound I journal July 2012
Parallel and Competitive Pathways for Substrate Desaturation, Hydroxylation, and Radical Rearrangement by the Non-heme Diiron Hydroxylase AlkB journal December 2012
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Cytochrome P450-Catalyzed Hydroxylation of Mechanistic Probes that Distinguish between Radicals and Cations. Evidence for Cationic but Not for Radical Intermediates journal March 2000
A Common Late-Stage Intermediate in Catalysis by 2-Hydroxyethyl-phosphonate Dioxygenase and Methylphosphonate Synthase journal February 2015
Decarboxylation of Fatty Acids to Terminal Alkenes by Cytochrome P450 Compound I journal April 2015
Manganese-Catalyzed Late-Stage Aliphatic C–H Azidation journal April 2015
Experimental Correlation of Substrate Position with Reaction Outcome in the Aliphatic Halogenase, SyrB2 journal May 2015
Mechanism of Oxygen Activation in a Flavin-Dependent Monooxygenase: A Nearly Barrierless Formation of C4a-Hydroperoxyflavin via Proton-Coupled Electron Transfer journal July 2015
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Modeling Non-Heme Iron Halogenases: High-Spin Oxoiron(IV)–Halide Complexes That Halogenate C–H Bonds journal February 2016
Spectroscopic Evidence for the Two C–H-Cleaving Intermediates of Aspergillus nidulans Isopenicillin N Synthase journal July 2016
The Cytochrome P450-Catalyzed Oxidative Rearrangement in the Final Step of Pentalenolactone Biosynthesis: Substrate Structure Determines Mechanism journal September 2016
Radicals: Reactive Intermediates with Translational Potential journal September 2016
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Versatility of biological non-heme Fe(II) centers in oxygen activation reactions journal February 2008
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