A new strategy to efficiently cleave and form C–H bonds using proton-coupled electron transfer

Markle, Todd F.; Darcy, Julia W.; Mayer, James M.

doi:10.1126/sciadv.aat5776

Cited by 66 publications

(175 citation statements)

References 37 publications

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“…(B) Plot of log( k MS-CPET ) vs log( K eq ). Part (A) reproduced and part (B) adapted with permission from ref 35. Copyright The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science.…”

Section: Figurementioning

confidence: 99%

“…35 At the outset of this Account, we showed examples of PCET at C—H bonds that generally fell into definitions for HAT. However, all of the examples of MS-CPET given above, and all prior reports of MS-CPET reactions, require the initial formation of a hydrogen bond.…”

Section: Introductionmentioning

confidence: 97%

“…35 Mechanistic studies indicated that the rate-determining step is MS-CPET to form a reactive carbon-centered radical, by PT to the carboxylate base concerted with ET to the oxidant. The fluorenyl radical then rapidly undergoes oxidative deprotonation and cyclization to form the lactone.…”

Section: Introductionmentioning

confidence: 99%

“…It is therefore likely that enzymatic systems utilize MS-CPET mechanisms to make and break C—H bonds, and we have suggested a specific example, the hydrogenation of a porphyrin C = C bond in the biosynthesis of chlorophyll. 35 …”

Section: Introductionmentioning

confidence: 99%

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A Continuum of Proton-Coupled Electron Transfer Reactivity

et al. 2018

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CONSPECTUS: Proton-coupled electron transfer (PCET) covers a wide range of reactions involving the transfer(s) of electrons and protons. The best-known PCET reaction, hydrogen atom transfer (HAT), has been studied in detail for more than a century. HAT is generally described as the concerted transfer of a hydrogen atom (H• ≡ H+ + e−) from one group to another, Y + H−X → Y−H + X, but a strict definition of HAT has been difficult to establish. Distinctions are more challenging when the transfer of “H•” involves e− and H+ that transfer to/from spatially distinct sites or even completely separate reagents (multiple-site concerted proton−electron transfer, MS-CPET). MS-CPET reactivity is increasingly proposed in biological and synthetic contexts, and some reactions typically described as HAT more resemble MS-CPET. Despite that HAT and MS-CPET reactions “look different,” we argue here that these reactions lie on a reactivity continuum, and that they are governed by many of the same key parameters. This Account walks the reader across this PCET reactivity continuum, using a series of studies to show the strong similarities of reactions that move protons and electrons in seemingly different ways. To prepare for our stroll, we describe the thermochemical and kinetic frameworks for HAT and MS-CPET. The driving force for a solution HAT reaction is most easily discussed as the difference in the bond dissociation free energies (BDFEs) of the reactants and products. BDFEs can be analyzed as sums of electron and proton transfer steps and can therefore be obtained from pKa and E° values. Even though MS-CPET reactions do not make and break H−X bonds in the same way as HAT, the same thermochemical description can be used with the introduction of an effective BDFE (BDFEeff). The BDFEeff of a reductant/acid pair is the free energy of that pair to form H•, which can be obtained from pKa and E° values in an analogous fashion to a standard BDFE. When the PCET thermochemistry is known, HAT and PCET rate constants can be understood and often predicted using linear free energy relationships (the Brønsted catalysis law) and Marcus theory type approaches. After this background, we walk the reader through a continuum of PCET reactivity. Our journey begins with a study of metalmediated HAT from hydrocarbon substrates to a metal-oxo complex and travels to the MS-CPET end of the reactivity spectrum, involving the transfer of H+ and e− from the hydroxylamine TEMPOH to two completely separate molecules. These examples, and those in between, are all analyzed within the same thermodynamic and kinetic framework. A description of the first examples of MS-CPET with C−H bonds uses the same framework and highlights the importance of hydrogen bonding and preorganization. The examples and analyses show that the reactions along the PCET continuum are more similar than they are different, and that attempts to divide these reactions into subcategories can obscure much of the essential chemistry. We hope that developing the many common features of these reac...

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Section: Figurementioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Continuum of Proton-Coupled Electron Transfer Reactivity

et al. 2018

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“…These values indicate that stretching of the O-H bond in TyrMe or NATyrME or of the N-H bond in TrpMe or NATrpME is not important in the transition state, strongly indicating that an asynchronous, electron rst, PCET mechanism is operating. [97][98][99][100][101][102] With respect to the compounds used in the present study, the substituted phenyl groups are not conjugated with the quinone system and the electronic effect of the substituted phenyl group is therefore limited to a possible inductive effect upon the furano-or pyrano-ring oxygen. In a general manner, the quenching rate constants by indolic quenchers and 4methoxyphenol are larger than the quenching rate constants for the tyrosine derivatives, phenol and 4-cyanophenol reecting the more electron rich nature of the indolic derivatives.…”

Section: A Quenching Of Naphthoquinonesmentioning

confidence: 99%

A photochemical and theoretical study of the triplet reactivity of furano- and pyrano-1,4-naphthoquionones towards tyrosine and tryptophan derivatives

et al. 2019

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Gas‐Phase Mechanism of O^.−/Ni²⁺‐Mediated Methane Conversion to Formaldehyde

Müller

Schöllkopf

et al. 2022

Angewandte Chemie

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The gas-phase reaction of NiAl 2 O 4 + with CH 4 is studied by mass spectrometry in combination with vibrational action spectroscopy and density functional theory (DFT). Two product ions, NiAl 2 O 4 H + and NiAl 2 O 3 H 2 + , are identified in the mass spectra. The DFT calculations predict that the global minimumenergy isomer of NiAl 2 O 4 + contains Ni in the + II oxidation state and features a terminal AlÀ O *À oxygen radical site. They show that methane can react along two competing pathways leading to formation of either a methyl radical (CH 3 * ) or formaldehyde (CH 2 O). Both reactions are initiated by hydrogen atom transfer from methane to the terminal O *À site, followed by either CH 3 * loss or CH 3 * migration to an O 2À site next to the Ni 2 + center. The CH 3 * attaches as CH 3 + to O 2À and its unpaired electron is transferred to the Ni-center reducing it to Ni + . The proposed mechanism is experimentally confirmed by vibrational spectroscopy of the reactant and two different product ions.

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A new strategy to efficiently cleave and form C–H bonds using proton-coupled electron transfer

Abstract: A new reaction for carbon: Separating the electron and proton allows C–H bonds to be cleaved and formed with mild reagents.

Cited by 66 publications

References 37 publications

A Continuum of Proton-Coupled Electron Transfer Reactivity

A Continuum of Proton-Coupled Electron Transfer Reactivity

A photochemical and theoretical study of the triplet reactivity of furano- and pyrano-1,4-naphthoquionones towards tyrosine and tryptophan derivatives

Gas‐Phase Mechanism of O^.−/Ni²⁺‐Mediated Methane Conversion to Formaldehyde

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A new strategy to efficiently cleave and form C–H bonds using proton-coupled electron transfer

Abstract: A new reaction for carbon: Separating the electron and proton allows C–H bonds to be cleaved and formed with mild reagents.

Cited by 66 publications

References 37 publications

A Continuum of Proton-Coupled Electron Transfer Reactivity

A Continuum of Proton-Coupled Electron Transfer Reactivity

A photochemical and theoretical study of the triplet reactivity of furano- and pyrano-1,4-naphthoquionones towards tyrosine and tryptophan derivatives

Gas‐Phase Mechanism of O.−/Ni2+‐Mediated Methane Conversion to Formaldehyde

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Gas‐Phase Mechanism of O^.−/Ni²⁺‐Mediated Methane Conversion to Formaldehyde