Selective C–H halogenation over hydroxylation by non-heme iron(iv)-oxo

Despite the growing interest in the synthesis of fluorinated organic compounds, few methods are able to incorporate fluoride ion directly into alkyl C-H bonds. Here, we report the C(sp3)-H fluorination reactivity of a formally copper(III) fluoride complex. The C-H fluorination intermediate, LCuF, along with its chloride and bromide analogs, LCuCl and LCuBr, were prepared directly from halide sources with a chemical oxidant and fully characterized. While all three copper(III) halide complexes capture carbon radicals efficiently to afford C(sp3)-halogen bonds, LCuF is two orders of magnitude more efficient at hydrogen atom abstraction (HAA) than LCuCl and LCuBr. Alongside reported kinetic data for other LCu(III) species, we established a positive correlation between ligand basicity and the rate of HAA. The capability of LCuF to perform both hydrogen atom abstraction and radical capture was leveraged to enable fluorination of allylic and benzylic C-H bonds and α-C-H bonds of ethers at room temperature.

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Energetics of non-heme iron reactivity: can ab initio calculations provide the right answer?

Physical Chemistry Chemical Physics ◽

10.1039/d0cp04401f ◽

2020 ◽

Vol 22 (41) ◽

pp. 23908-23919

Author(s):

Milica Feldt ◽

Carlos Martín-Fernández ◽

Jeremy N. Harvey

Keyword(s):

Hydrogen Atom ◽

Ab Initio Calculations ◽

Ab Initio ◽

Computational Methods ◽

Hydrogen Atom Transfer ◽

Heme Iron ◽

Reaction Pathways ◽

Non Heme Iron ◽

Epoxidation Reaction ◽

The Right

We use a variety of computational methods to characterize and compare the hydrogen atom transfer (HAT) and epoxidation reaction pathways for oxidation of cyclohexene by an iron(iv)-oxo complex.

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Iron (II/III) Halide Complexes Promote the Interconversion of Nitric Oxide and S-nitrosothiols through Reversible Fe-S Interaction

10.26434/chemrxiv.13951274 ◽

2021 ◽

Author(s):

Anna Poptic ◽

Shiyu Zhang

Keyword(s):

Nitric Oxide ◽

Bond Formation ◽

Spectroscopic Studies ◽

Heme Iron ◽

Chloride Complexes ◽

Physiological Processes ◽

Non Heme Iron ◽

Halide Complexes ◽

Labile Iron

Heme and non-heme iron in biology mediate the storage/release of NO• from S-nitrosothiols as a means to control the biological concentration of NO•. Despite their importance in many physiological processes, the mechanisms of N-S bond formation/cleavage at Fe centers have been controversial. Herein, we report the interconversion of NO• and S-nitrosothiols mediated by FeII/FeIII chloride complexes. The reaction of two equivalents of S-nitrosothiol (Ph3CSNO) with [Cl6FeII2]2- results in facile release of NO• and formation of iron(III) halothiolate. Detailed spectroscopic studies, including in situ UV-vis, IR, and Mössbauer spectroscopy, support the interaction of the S−atom with the FeII center. This is in contrast to the proposed mechanism of NO• release from the well-studied “red product” k1-N bound S-nitrosothiol FeII complex, [(CN)5Fe(k1-N-RSNO)]3-. Additionally, FeIII chloride can mediate NO• storage through the formation of S-nitrosothiols. Treatment of iron(III) halothiolate with two equivalents of NO• regenerates Ph3CSNO with the FeII source trapped as the S = 3/2 {FeNO}7 species [Cl3FeNO]-, which is inert towards further coordination and activation of S-nitrosothiols. Our work demonstrates how labile iron can mediate the interconversion of NO•/thiolate and S-nitrosothiol, which has important implications for how Nature manages the biological concentration of free NO•.

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Modeling Non-Heme Iron Halogenases: High-Spin Oxoiron(IV)–Halide Complexes That Halogenate C–H Bonds

Journal of the American Chemical Society ◽

10.1021/jacs.5b11511 ◽

2016 ◽

Vol 138 (8) ◽

pp. 2484-2487 ◽

Cited By ~ 45

Author(s):

Mayank Puri ◽

Achintesh N. Biswas ◽

Ruixi Fan ◽

Yisong Guo ◽

Lawrence Que

Keyword(s):

High Spin ◽

Heme Iron ◽

Non Heme Iron ◽

Halide Complexes

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C(sp3)-H Fluorination with a Copper(II)/(III) Redox Couple

10.26434/chemrxiv.11919093.v1 ◽

2020 ◽

Author(s):

Jamey Bower ◽

Andrew Cypcar ◽

Brenda Henriquez ◽

S. Chantal E. Stieber ◽

Shiyu Zhang

Keyword(s):

Hydrogen Atom ◽

Organic Compounds ◽

Kinetic Data ◽

Room Temperature ◽

Hydrogen Atom Abstraction ◽

Fluoride Ion ◽

Halogen Bonds ◽

Fluoride Complex ◽

Carbon Radicals ◽

Halide Complexes

Despite the growing interest in the synthesis of fluorinated organic compounds, few methods are able to incorporate fluoride ion directly into alkyl C-H bonds. Here, we report the C(sp3)-H fluorination reactivity of a formally copper(III) fluoride complex. The C-H fluorination intermediate, LCuF, along with its chloride and bromide analogs, LCuCl and LCuBr, were prepared directly from halide sources with a chemical oxidant and fully characterized. While all three copper(III) halide complexes capture carbon radicals efficiently to afford C(sp3)-halogen bonds, LCuF is two orders of magnitude more efficient at hydrogen atom abstraction (HAA) than LCuCl and LCuBr. Alongside reported kinetic data for other LCu(III) species, we established a positive correlation between ligand basicity and the rate of HAA. The capability of LCuF to perform both hydrogen atom abstraction and radical capture was leveraged to enable fluorination of allylic and benzylic C-H bonds and α-C-H bonds of ethers at room temperature.

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Iron (II/III) Halide Complexes Promote the Interconversion of Nitric Oxide and S-nitrosothiols through Reversible Fe-S Interaction

10.26434/chemrxiv.13951274.v1 ◽

2021 ◽

Author(s):

Anna Poptic ◽

Shiyu Zhang

Keyword(s):

Nitric Oxide ◽

Bond Formation ◽

Spectroscopic Studies ◽

Heme Iron ◽

Chloride Complexes ◽

Physiological Processes ◽

Non Heme Iron ◽

Halide Complexes ◽

Labile Iron

Heme and non-heme iron in biology mediate the storage/release of NO• from S-nitrosothiols as a means to control the biological concentration of NO•. Despite their importance in many physiological processes, the mechanisms of N-S bond formation/cleavage at Fe centers have been controversial. Herein, we report the interconversion of NO• and S-nitrosothiols mediated by FeII/FeIII chloride complexes. The reaction of two equivalents of S-nitrosothiol (Ph3CSNO) with [Cl6FeII2]2- results in facile release of NO• and formation of iron(III) halothiolate. Detailed spectroscopic studies, including in situ UV-vis, IR, and Mössbauer spectroscopy, support the interaction of the S−atom with the FeII center. This is in contrast to the proposed mechanism of NO• release from the well-studied “red product” k1-N bound S-nitrosothiol FeII complex, [(CN)5Fe(k1-N-RSNO)]3-. Additionally, FeIII chloride can mediate NO• storage through the formation of S-nitrosothiols. Treatment of iron(III) halothiolate with two equivalents of NO• regenerates Ph3CSNO with the FeII source trapped as the S = 3/2 {FeNO}7 species [Cl3FeNO]-, which is inert towards further coordination and activation of S-nitrosothiols. Our work demonstrates how labile iron can mediate the interconversion of NO•/thiolate and S-nitrosothiol, which has important implications for how Nature manages the biological concentration of free NO•.

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Mechanistic Borderline of One-Step Hydrogen Atom Transfer versus Stepwise Sc3+-Coupled Electron Transfer from Benzyl Alcohol Derivatives to a Non-Heme Iron(IV)-Oxo Complex

Inorganic Chemistry ◽

10.1021/ic3016723 ◽

2012 ◽

Vol 51 (18) ◽

pp. 10025-10036 ◽

Cited By ~ 53

Author(s):

Yuma Morimoto ◽

Jiyun Park ◽

Tomoyoshi Suenobu ◽

Yong-Min Lee ◽

Wonwoo Nam ◽

...

Keyword(s):

Electron Transfer ◽

Hydrogen Atom ◽

Benzyl Alcohol ◽

Hydrogen Atom Transfer ◽

Heme Iron ◽

Atom Transfer ◽

Non Heme Iron ◽

One Step

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Strongly Coupled Redox-Linked Conformational Switching at the Active Site of the Non-Heme Iron-Dependent Dioxygenase, TauD

10.26434/chemrxiv.9461462 ◽

2019 ◽

Author(s):

Christopher John ◽

Greg M. Swain ◽

Robert P. Hausinger ◽

Denis A. Proshlyakov

Keyword(s):

Active Site ◽

Structural Model ◽

Heme Iron ◽

Chemical Transformations ◽

Experimental Conditions ◽

Strongly Coupled ◽

Non Heme Iron ◽

Reversible Redox ◽

Wide Range ◽

Complex Structural

2-Oxoglutarate (2OG)-dependent dioxygenases catalyze C-H activation while performing a wide range of chemical transformations. In contrast to their heme analogues, non-heme iron centers afford greater structural flexibility with important implications for their diverse catalytic mechanisms. We characterize an in situ structural model of the putative transient ferric intermediate of 2OG:taurine dioxygenase (TauD) by using a combination of spectroelectrochemical and semi-empirical computational methods, demonstrating that the Fe (III/II) transition involves a substantial, fully reversible, redox-linked conformational change at the active site. This rearrangement alters the apparent redox potential of the active site between -127 mV for reduction of the ferric state and 171 mV for oxidation of the ferrous state of the 2OG-Fe-TauD complex. Structural perturbations exhibit limited sensitivity to mediator concentrations and potential pulse duration. Similar changes were observed in the Fe-TauD and taurine-2OG-Fe-TauD complexes, thus attributing the reorganization to the protein moiety rather than the cosubstrates. Redox difference infrared spectra indicate a reorganization of the protein backbone in addition to the involvement of carboxylate and histidine ligands. Quantitative modeling of the transient redox response using two alternative reaction schemes across a variety of experimental conditions strongly supports the proposal for intrinsic protein reorganization as the origin of the experimental observations.

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