Radical Cation Salts: From Single-Electron Oxidation to C–H Activation­

Jia, Xiaodong

doi:10.1055/s-0035-1560509

Cited by 22 publications

(14 citation statements)

References 7 publications

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“…The use of oxidant/reductant is a well-known practice in chemistry to promote a reaction . In C–H activation, this is also commonly applied due to the relatively large BDEs of C–H bonds, but the role of oxidation/reduction in affecting the bond activation mechanisms has usually not been paid much attention until a recent surge of photoredox catalysis. − The effect of a single-electron transfer (SET) on weakening a C–H bond can, in fact, be measured in terms of bond energetic changes upon an elementary SET reaction by using the thermochemical cycles as exemplified in Scheme developed by Bordwell and co-workers for radical cations, ,,− where the p K a and electrode data can be readily obtained in solution. − The BDE of radical anions can be derived similarly …”

Section: Briefs On Methods Of Bond Energy Determinationmentioning

confidence: 99%

“…Normally, the two sequential steps are not separable due to the huge energetic driving force for CH +• to collapse to C· and H + , as obvious from the Δp K a (CH–CH +• ) gaps in Table . In some photoredox-catalyzed bond activations, this reaction path has already been recognized. − Although in thermal processes an unambiguous single-electron transfer (SET) may not always be detected, interactions between a metal–oxo complex and a substrate would still make the C–H bond quasi-activated, the trend of which to undergo reaction can be expected to follow the same pattern. However, this does not necessarily rule out other pathways, like e–H· or e–H + –e (ends up in a H – transfer) under some conditions, and thus offers a chance for rational manipulations of certain key factors toward desired reactions.…”

Section: Conclusion and Outlookmentioning

confidence: 99%

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The Essential Role of Bond Energetics in C–H Activation/Functionalization

et al. 2017

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The most fundamental concepts in chemistry are structure, energetics, reactivity and their inter-relationships, which are indispensable for promoting chemistry into a rational science. In this regard, bond energy, the intrinsic determinant directly related to structure and reactivity, should be most essential in serving as a quantitative basis for the design and understanding of organic transformations. Although C-H activation/functionalization have drawn tremendous research attention and flourished during the past decades, understanding the governing rules of bond energetics in these processes is still fragmentary and seems applicable only to limited cases, such as metal-oxo-mediated hydrogen atom abstraction. Despite the complexity of C-H activation/functionalization and the difficulties in measuring bond energies both for the substrates and intermediates, this is definitely a very important issue that should be more generally contemplated. To this end, this review is rooted in the energetic aspects of C-H activation/functionalization, which were previously rarely discussed in detail. Starting with a concise but necessary introduction of various classical methods for measuring heterolytic and homolytic energies for C-H bonds, the present review provides examples that applied the concept and values of C-H bond energy in rationalizing the observations associated with reactivity and/or selectivity in C-H activation/functionalization.

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Section: Briefs On Methods Of Bond Energy Determinationmentioning

confidence: 99%

Section: Conclusion and Outlookmentioning

confidence: 99%

The Essential Role of Bond Energetics in C–H Activation/Functionalization

et al. 2017

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“…We expected that the photoexcited D−π–D system undergoes SET to electron acceptors such as electron-accepting fluoroalkylating reagents ( + R F ) to generate hole-activated [D−π–D] •+ and fluoroalkyl radicals ( • R F ). Because triarylaminium salts are known as strong 1e-oxidants, the cationic radical species of 1 is also anticipated to show 1e-oxidizing ability, associated with regeneration of 1 in the ground state (Scheme (b)). As mentioned above, 9,10-bis(diarylamino)anthracenes ( 1 ) are latent organic photoredox catalysts with high reducing power.…”

Section: Introductionmentioning

confidence: 99%

Strongly Reducing (Diarylamino)anthracene Catalyst for Metal-Free Visible-Light Photocatalytic Fluoroalkylation

et al. 2018

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Well-defined 9,10-bis(di(p-tert-butylphenyl)amino)anthracene serves as a photocatalyst for radical fluoroalkylation under visible light irradiation. The diarylamine (Donor)–anthracene (π conjugated system)–diarylamine (Donor) scaffolds are easily accessed by typical palladium-catalyzed cross-coupling protocols of the corresponding halogenated anthracenes with various lithium diarylamides. The anthracene-based photocatalyst exhibits high reducing power, leading to generation of versatile fluoroalkyl radicals such as tri- and difluoroethyl and tri- and difluoromethyl radicals from the corresponding electron-accepting precursors. Catalyst design strongly influences the absorption capability of visible light and stability toward redox stimuli. The detailed mechanistic studies on the metal-free photocatalytic amino-trifluoroethylation of styrene with diphenyl(2,2,2-trifluoroethyl)sulfonium trifluoromethanesulfonate suggest that the reaction proceeds via catalytic radical processes rather than radical chain processes. In addition, the static quenching process is involved in the first single-electron-transfer (SET) process from the photocatalyst to the fluoroalkylating reagent. Furthermore, the 1e-oxidized cationic radical species of 9,10-bis(di(p-tert-butylphenyl)amino)anthracene, a key active catalytic species with long lifetime and a characteristic IVCT (Intervalence Charge Transfer) band in the near IR (NIR) region, is detected. From the viewpoint of elemental strategy initiative and green chemistry, the present noble metal-free organic photocatalytic system provides a pivotal technology to replace ruthenium- and iridium-based metal photocatalysis.

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“…The addition of incremental amounts of sodium cyanide (up to 2 equiv) to the previous solution caused an increase of the anodic current which is no longer under diffusion control . The effect of cyanide on the voltammetric profile of (+)- 6a is attributed to the presence of a typical catalytic current due to the return of the aminium radical cation A to its neutral form which occurred during the homogeneous redox process (Table , top) in which the cyanide anion is now oxidized at a lower potential than that required for its direct oxidation at the electrode surface . The magnitude of such process is given by the value of the i p / i p 0 ratio (where i p and i p 0 represent the anodic currents in the presence and in the absence of sodium cyanide, respectively).…”

Section: Resultsmentioning

confidence: 99%

Synthesis of Tetrahydroisoquinoline Alkaloids and Related Compounds through the Alkylation of Anodically Prepared α-Amino Nitriles

et al. 2016

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α-Amino nitrile 2a was conveniently prepared in two individual steps from chiral hexafluorophosphate salt isoquinolinium (-)-8b including anodic cyanation as an efficient means to activate the sp(3) C1-H bond of the THIQ nucleus. The lithiation of 2a was carried out in THF at -80 °C in the presence of LDA to produce a stable α-amino carbanion which was condensed on a large variety of alkyl halides. The resulting quaternary α-amino nitriles were subjected to a stereoselective reductive decyanation in ethanol in the presence of NaBH4 as the hydride donor to yield N-Boc-1-alkyl-THIQs (+)-10a-g in up to 97:3 er's after removal of the chiral auxiliary group. Examination of the ORTEP view of THIQ (+)-1f revealed that the newly created stereogenic center had an absolute S configuration. Likewise, (-)-xylopinine was synthesized in four workup steps in an overall 63% yield from α-amino nitrile (+)-2b. In this process, crystallization of an enantioenriched mixture (90:10) of (-)-norlaudanosine with 1 equiv of (-)-N-acetyl-l-leucine afforded the leucinate salt (+)-13 (99:1 dr). Similarly, (+)-salsolidine was displaced from its (-)-DBTA salt (-)-12 in 99:1 er, which was determined by proton and carbon NMR spectroscopy in the presence of thiophosphinic acid (+)-14 as the chiral solvating agent.

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Radical Cation Salts: From Single-Electron Oxidation to C–H Activation

Cited by 22 publications

References 7 publications

The Essential Role of Bond Energetics in C–H Activation/Functionalization

The Essential Role of Bond Energetics in C–H Activation/Functionalization

Strongly Reducing (Diarylamino)anthracene Catalyst for Metal-Free Visible-Light Photocatalytic Fluoroalkylation

Synthesis of Tetrahydroisoquinoline Alkaloids and Related Compounds through the Alkylation of Anodically Prepared α-Amino Nitriles

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Radical Cation Salts: From Single-Electron Oxidation to C–H Activation­

Cited by 22 publications

References 7 publications

The Essential Role of Bond Energetics in C–H Activation/Functionalization

The Essential Role of Bond Energetics in C–H Activation/Functionalization

Strongly Reducing (Diarylamino)anthracene Catalyst for Metal-Free Visible-Light Photocatalytic Fluoroalkylation

Synthesis of Tetrahydroisoquinoline Alkaloids and Related Compounds through the Alkylation of Anodically Prepared α-Amino Nitriles

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Radical Cation Salts: From Single-Electron Oxidation to C–H Activation