Electrocatalysis as an enabling technology for organic synthesis

Chemical Society Reviews, Год журнала: 2021, Номер 50(14), С. 7941 - 8002

Опубликована: Янв. 1, 2021

Electrochemistry has recently gained increased attention as a versatile strategy for achieving challenging transformations at the forefront of synthetic organic chemistry. Electrochemistry's unique ability to generate highly reactive radical and ion intermediates in controlled fashion under mild conditions inspired development number new electrochemical methodologies preparation valuable chemical motifs. Particularly, recent developments electrosynthesis have featured an use redox-active electrocatalysts further enhance control over selective formation downstream reactivity these intermediates. Furthermore, electrocatalytic mediators enable proceed manner that is mechanistically distinct from purely methods, allowing subversion kinetic thermodynamic obstacles encountered conventional synthesis. This review highlights key innovations within past decade area electrocatalysis, with emphasis on mechanisms catalyst design principles underpinning advancements. A host oxidative reductive are discussed grouped according classification transformation nature electrocatalyst.

Язык: Английский

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Electrochemical Oxidative Cross-Coupling with Hydrogen Evolution Reactions

Accounts of Chemical Research, Год журнала: 2019, Номер 52(12), С. 3309 - 3324

Опубликована: Ноя. 27, 2019

Oxidative cross-coupling has proved to be one of the most straightforward strategies for forming carbon-carbon and carbon-heteroatom bonds from easily available precursors. Over past two decades, tremendous efforts have been devoted in this field significant advances achieved. However, order remove surplus electrons substrates chemical formation, stoichiometric oxidants are usually needed. Along with development modern sustainable chemistry, considerable perform oxidative reactions under external-oxidant-free conditions. Electrochemical synthesis is a powerful environmentally benign approach, which can not only achieve cross-couplings conditions, but also release valuable hydrogen gas during bond formation. Recently, electrochemical evolution significantly explored. This Account presents our recent toward reactions. (1) We explored thiols/thiophenols arenes, heteroarenes, alkenes C-S (2) Using strategy C-H/N-H evolution, we successfully realized C-H amination phenols, anilines, imidazopyridines, even ethers. (3) Employing halide salts as green halogenating reagents, developed clean halogenation protocol oxidation To address limitation that reaction had carry out aqueous solvent, an alternative method uses CBr4, CHBr3, CH2Br2, CCl3Br, CCl4 reagents mixture acetonitrile methanol cosolvent. (4) approach constructing C-O well-developed manner. (5) Under mild C(sp2)-H C(sp3)-H phosphonylation modest high yields. (6) achieved S-H/S-H By anodic instead oxidants, overoxidation thiols thiophenols was well avoided. (7) The methods structurally diverse heterocyclic compounds were via annulations. (8) applied difunctionalization multiple step, such C-S/C-O bonds, C-S/C-N C-Se/C-O C-Se/C-N bonds. hope studies will stimulate research interest chemists pave way discovery more

Язык: Английский

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Site-Selective C–H Functionalization via Synergistic Use of Electrochemistry and Transition Metal Catalysis

Accounts of Chemical Research, Год журнала: 2020, Номер 53(2), С. 300 - 310

Опубликована: Янв. 15, 2020

Electrochemical synthesis of organic compounds has emerged as an attractive and environmentally benign alternative to conventional approaches for oxidation reduction that utilizes electric current instead chemical oxidants reductants. As such, many useful transformations have been developed, including the Kolbe reaction, Simons fluorination process, Monsanto adiponitrile Shono oxidation, name a few. C-H functionalization represents one most promising reaction types among electrochemical transformations, since this process avoids prefunctionalization substrates provides novel retrosynthetic disconnections. However, site-selective anodic bonds is still fundamental challenge due high potentials compared solvents common functional groups. To overcome issue, indirect electrolysis via action mediator (a redox catalyst) regularly employed, by which selectivity can be controlled following said with substrate. Since transition metal complexes easily tuned modification ligand, synergistic use electrochemistry catalysis achieve strategy. In Account, we summarize contextualize our recent efforts toward metal-catalyzed proximal suitable directing group. We developed oxygenation, acylation, alkylation, halogenation reactions in Pd(II) species oxidized Pd(III) or Pd(IV) intermediate followed reductive elimination form corresponding C-O, C-C, C-X bonds. Importantly, improved monofunctionalization achieved Pd-catalyzed C(sp3)-H oxygenation using PhI(OAc)2 oxidant. Physical separators are sometimes used prevent deposition Pd black on cathode resulting from valent species. skirted issue through development Cu-catalyzed C(sp2)-H amination n-Bu4NI cocatalyst undivided cell. addition, Ir-catalyzed vinylic acrylic acids alkynes cell, affording various substituted α-pyrones good excellent yield. More importantly, oxidants, Ag2CO3, Cu(OAc)2, PhI(OAc)2, resulted much lower yields absence electrical under otherwise identical conditions. elaborated below, progress area effective platform friendly sustainable selective transformations.

Язык: Английский

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A Survival Guide for the “Electro-curious”

Accounts of Chemical Research, Год журнала: 2019, Номер 53(1), С. 72 - 83

Опубликована: Дек. 11, 2019

ConspectusThe appeal and promise of synthetic organic electrochemistry have been appreciated over the past century. In terms redox chemistry, which is frequently encountered when forging new bonds, it difficult to conceive a more economical way add or remove electrons than electrochemistry. Indeed, many largest industrial chemical processes are achieved in practical using as reagent. Why then, after so years documented benefits electrochemistry, not widely embraced by mainstream practitioners? Erroneous perceptions that "black box" combined with lack intuitive inexpensive standardized equipment likely contributed this stagnation interest within community. This barrier entry magnified fact can already be accomplished simple reagents even if they less atom-economic. Time has proven sustainability economics strong enough driving forces for adoption electrochemical techniques broader like chemists dabbled age-old technique, our first foray into area was choice but rather through sheer necessity.The unique reactivity old redox-modulating technique must therefore highlighted leveraged order draw field. Enabling bonds forged higher levels chemo- regioselectivity will accomplish goal. doing so, envisioned widespread go beyond supplanting unsustainable mundane reactions development exciting paradigms enable heretofore unimagined retrosynthetic pathways. Whereas rigorous physical principles electroorganic synthesis reviewed elsewhere, often case such summaries leave out pragmatic aspects designing, optimizing, scaling up preparative reactions. Taken together, task setting an reaction, much inventing one, vexing seasoned chemists. Account features format focuses on addressing exact issue context own studies. The graphically rich presentation style pinpoints basic concepts, typical challenges, key insights those "electro-curious" who seek rapidly explore power their research.

Язык: Английский

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Metalla-electrocatalyzed C–H Activation by Earth-Abundant 3d Metals and Beyond

Accounts of Chemical Research, Год журнала: 2019, Номер 53(1), С. 84 - 104

Опубликована: Дек. 19, 2019

To improve the efficacy of molecular syntheses, researchers wish to capitalize upon selective modification otherwise inert C-H bonds. The past two decades have witnessed considerable advances in coordination chemistry that set stage for transformative tools functionalizations. Particularly, oxidative C-H/C-H and C-H/Het-H transformations gained major attention because they avoid all elements substrate prefunctionalization. Despite advances, activations been dominated by precious transition metal catalysts based on palladium, ruthenium, iridium, rhodium, thus compromising sustainable nature overall activation approach. same holds true predominant use stoichiometric chemical oxidants regeneration active catalyst, prominently featuring hypervalent iodine(III), copper(II), silver(I) oxidants. Thereby, quantities undesired byproducts are generated, which preventive applications scale. In contrast, elegant merger homogeneous metal-catalyzed with electrosynthesis bears unique power achieve outstanding levels oxidant resource economy. Thus, contrast classical electrosyntheses control, metalla-electrocatalysis huge largely untapped potential unmet site selectivities means catalyst control. While indirect electrolysis using palladium complexes has realized, less toxic expensive base feature distinct beneficial assets toward this Account, I summarize emergence electrocatalyzed earth-abundant 3d metals beyond, a topical focus contributions from our laboratories through November 2019. cobalt electrocatalysis was identified as particularly powerful platform wealth transformations, including oxygenations nitrogenations well alkynes, alkenes, allenes, isocyanides, carbon monoxide, among others. As complementary tools, nickel, copper, very recently iron devised metalla-electrocatalyzed activations. Key success were detailed mechanistic insights, oxidation-induced reductive elimination scenarios. Likewise, development methods make weak O-coordination benefited crucial insights into catalyst's modes action experiment, operando spectroscopy, computation. Overall, thereby syntheses These electrooxidative frequently characterized improved chemoselectivities. Hence, ability dial redox at minimum level required desired transformation renders an ideal functionalization structurally complex molecules sensitive functional groups. This strategy was, inter alia, successfully applied scale-up continuous flow step-economical assembly polycyclic aromatic hydrocarbons.

Язык: Английский

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Electrochemical Oxidation of Organic Molecules at Lower Overpotential: Accessing Broader Functional Group Compatibility with Electron−Proton Transfer Mediators

Accounts of Chemical Research, Год журнала: 2020, Номер 53(3), С. 561 - 574

Опубликована: Фев. 12, 2020

ConspectusElectrochemical organic oxidation reactions are highly appealing because protons often effective terminal electron acceptors, thereby avoiding undesirable stoichiometric oxidants. These plagued by high overpotentials, however, that greatly limit their utility. Single-electron transfer (SET) from molecules generates high-energy radical-cations. Formation of such intermediates requires electrode potentials far above the thermodynamic reaction and frequently causes decomposition and/or side ancillary functional groups. In this Account, we show how electrocatalytic electron–proton mediators (EPTMs) address challenge. EPTMs bypass formation radical-cation supporting mechanisms operate at much lower (≥1 V) than those analogous direct electrolysis reactions.The stable aminoxyl radical TEMPO (2,2,6,6-tetramethylpiperidine N-oxyl) is an mediator for electrochemical alcohol oxidation, have employed processes applications ranging pharmaceutical synthesis to biomass conversion. A complementary method employs a cooperative Cu/TEMPO system operates 0.5 V potential TEMPO-only mediated process. This difference, which arises different catalytic mechanism, rationalizes broad group tolerance Cu/TEMPO-based aerobic catalysts.Aminoxyl long-standing challenges in "Shono oxidation," important α-C–H tertiary amides carbamates. Shono oxidations initiated high-potential SET step limits Aminoxyl-mediated Shono-type been developed tolerate diverse Analogous reactivity underlies cyanation secondary cyclic amines, new enables efficient diversification piperidine-based building blocks preparation non-natural amino acids.Electrochemical benzylic C–H bonds commonly generate arene cations, but methods again large overpotentials. Mediated promote hydrogen-atom-transfer (HAT) Fe-oxo species phthalimide N-oxyl (PINO) support oxygenation, iodination, oxidative-coupling reactions. merges photochemistry with electrochemistry achieve amidation C(sp3)–H bonds. unique process overpotentials compatible groups.These results implications electrochemistry, highlighting importance "overpotential" considerations prospects expanding synthetic utility using outer-sphere electron-transfer mechanisms. Principles demonstrated here equally relevant reductions.

Язык: Английский

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C–H activation

Nature Reviews Methods Primers, Год журнала: 2021, Номер 1(1)

Опубликована: Июнь 17, 2021

Язык: Английский

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Electrochemical oxidation of biomass derived 5-hydroxymethylfurfural (HMF): pathway, mechanism, catalysts and coupling reactions

Green Chemistry, Год журнала: 2021, Номер 23(12), С. 4228 - 4254

Опубликована: Янв. 1, 2021

HMF electrooxidation is emerging as a powerful and promising method to produce wide range of high-value chemicals on account mild operation conditions, controllable selectivity, scalability.

Язык: Английский

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Copper-Catalyzed Electrochemical C–H Amination of Arenes with Secondary Amines

Journal of the American Chemical Society, Год журнала: 2018, Номер 140(36), С. 11487 - 11494

Опубликована: Авг. 30, 2018

Electrochemical oxidation represents an environmentally friendly solution to conventional methods that require caustic stoichiometric chemical oxidants. However, C–H functionalizations merging transition-metal catalysis and electrochemical techniques are, date, largely confined the use of precious metals divided cells. Herein, we report first examples copper-catalyzed aminations arenes at room temperature using undivided cells, thereby providing a practical for construction arylamines. The n-Bu4NI as redox mediator is crucial this transformation. On basis mechanistic studies including kinetic profiles, isotope effects, cyclic voltammetric analyses, radical inhibition experiments, reaction appears proceed via single-electron-transfer (SET) process, high valent Cu(III) species likely involved. These findings provide new avenue transition-metal-catalyzed functionalization reactions mediators.

Язык: Английский

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Recent advances in organic electrosynthesis employing transition metal complexes as electrocatalysts

Science Bulletin, Год журнала: 2021, Номер 66(23), С. 2412 - 2429

Опубликована: Июль 13, 2021

Язык: Английский

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