Photons or Electrons? A Critical Comparison of Electrochemistry and Photoredox Catalysis for Organic Synthesis

Chemical Reviews, Год журнала: 2021, Номер 122(2), С. 2487 - 2649

Опубликована: Ноя. 9, 2021

Redox processes are at the heart of synthetic methods that rely on either electrochemistry or photoredox catalysis, but how do and catalysis compare? Both approaches provide access to high energy intermediates (e.g., radicals) enable bond formations not constrained by rules ionic 2 electron (e) mechanisms. Instead, they 1e mechanisms capable bypassing electronic steric limitations protecting group requirements, thus enabling chemists disconnect molecules in new different ways. However, while providing similar intermediates, differ several physical chemistry principles. Understanding those differences can be key designing transformations forging disconnections. This review aims highlight these similarities between comparing their underlying principles describing impact electrochemical photochemical methods.

Язык: Английский

---

Photochemical and Electrochemical Applications of Proton-Coupled Electron Transfer in Organic Synthesis

Chemical Reviews, Год журнала: 2021, Номер 122(2), С. 2017 - 2291

Опубликована: Ноя. 23, 2021

We present here a review of the photochemical and electrochemical applications multi-site proton-coupled electron transfer (MS-PCET) in organic synthesis. MS-PCETs are redox mechanisms which both an proton exchanged together, often concerted elementary step. As such, MS-PCET can function as non-classical mechanism for homolytic bond activation, providing opportunities to generate synthetically useful free radical intermediates directly from wide variety common functional groups. introduction practitioner’s guide reaction design, with emphasis on unique energetic selectivity features that characteristic this class. then chapters oxidative N–H, O–H, S–H, C–H homolysis methods, generation corresponding neutral species. Then, reductive PCET activations involving carbonyl, imine, other X═Y π-systems, heteroarenes, where ketyl, α-amino, heteroarene-derived radicals be generated. Finally, we asymmetric catalysis materials device applications. Within each chapter, subdivide by group undergoing homolysis, thereafter type transformation being promoted. Methods published prior end December 2020 presented.

Язык: Английский

---

Organic thermally activated delayed fluorescence (TADF) compounds used in photocatalysis

Chemical Society Reviews, Год журнала: 2021, Номер 50(13), С. 7587 - 7680

Опубликована: Янв. 1, 2021

Organic compounds that show Thermally Activated Delayed Fluorescence (TADF) have become wildly popular as next generation emitters in organic light-emitting diodes (OLEDs), but since 2016, received significant and increasing attention photocatalysts.

Язык: Английский

---

Photophysics and photochemistry with Earth-abundant metals – fundamentals and concepts

Chemical Society Reviews, Год журнала: 2020, Номер 49(4), С. 1057 - 1070

Опубликована: Янв. 1, 2020

Recent exciting developments in the area of mononuclear photoactive complexes with Earth-abundant metal ions (Cu, Zr, Fe, Cr) for potential eco-friendly applications (phosphorescent) organic light emitting diodes, imaging and sensing systems, dye-sensitized solar cells as photocatalysts are presented. Challenges, particular extension excited state lifetimes, recent conceptual breakthroughs substituting precious rare-Earth (e.g. Ru, Ir, Pt, Au, Eu) these by abundant outlined selected examples. Relevant fundamentals photophysics photochemistry discussed first, followed instructive case studies.

Язык: Английский

---

Potent Reductants via Electron-Primed Photoredox Catalysis: Unlocking Aryl Chlorides for Radical Coupling

Journal of the American Chemical Society, Год журнала: 2020, Номер 142(5), С. 2093 - 2099

Опубликована: Янв. 17, 2020

We describe a new catalytic strategy to transcend the energetic limitations of visible light by electrochemically priming photocatalyst prior excitation. This system is able productively engage aryl chlorides with reduction potentials hundreds millivolts beyond potential Na0 in productive radical coupling reactions. The radicals produced via this can be leveraged for both carbon–carbon and carbon–heteroatom bond-forming Through direct comparison, we illustrate reactivity selectivity advantages approach relative electrolysis photoredox catalysis.

Язык: Английский

---

Flow Photochemistry: Shine Some Light on Those Tubes!

Trends in Chemistry, Год журнала: 2019, Номер 2(2), С. 92 - 106

Опубликована: Ноя. 3, 2019

(Solar) Photochemistry in flow benefits from better, more uniform irradiation than batch, resulting shorter, selective reactions and efficient scale-up.Photochemical multiphasic fully exploit the photon- mass-transfer enhancement properties offered by chemistry.Flow photochemistry is gaining popularity pharmaceutical industry due to many advantages demonstrated chemistry itself large potential for automation. Continuous-flow has recently attracted significant interest chemists both academia working different disciplines backgrounds. Flow methods are now being used reaction discovery/methodology, scale-up production, rapid screening optimization. Photochemical processes currently an important research field scientific community recent exploitation of these methodologies made clear its importance modern technology worldwide. This review highlights most features continuous-flow applied photochemical provides a general perspective on this rapidly evolving field. The use light promote chemical been exploited since 18th century, but only resurgence observed synthetic organic chemistry, particular development visible-light photoredox catalysis [1McAtee R.C. et al.Illuminating catalysis.Trends Chem. 2019; 1: 111-125Abstract Full Text PDF Scopus (127) Google Scholar, 2Kancherla R. al.Visible light-induced excited-state transition-metal 510-523Abstract (47) 3Romero N.A. Nicewicz D.A. Organic catalysis.Chem. Rev. 2016; 116: 10075-10166Crossref PubMed (2316) 4Hockin B.M. al.Photoredox catalysts based earth-abundant metal complexes.Catal. Sci. Technol. 9: 889-915Crossref 5Riente P. Noel T. Application oxide semiconductors light-driven transformations.Catal. 5186-5232Crossref Scholar]. All transformations involving (e.g., Figure 1A–D) must consider, besides classical parameters (i.e., conditions), photophysical aspects sensitizer (see Glossary)/photocatalyst (when used), reactor design. latter, although often neglected chemists, critical aspect outcome studied transformation. includes, example, size, shape, material vessel, characteristics positioning source(s), heat-transfer properties, particularly when high-intensity lamps [6Noël Processes Continuous-Flow Reactors. World Scientific, 2017Crossref 7Guba F. al.Rapid prototyping engineering.Chem. Ing. Tech. 91: 17-29Google engineering technological at basis irreproducibility non-scalability such transformations. According Beer–Lambert law, transmittance decreases exponentially with distance source (Figure 1F). For standard batch (diameter least centimeter range), intensity considerably flask walls middle mixture, slow nonhomogeneous mixture. Performing microchannels (ID < 1 mm) allows higher homogeneous photon flux, shorter times consequently less side-product formation over-irradiation, [8Cambié D. al.Applications synthesis, science, water treatment.Chem. 10276-10341Crossref (744) 9Noël A personal future photochemistry.J. 2017; 7: 87-93Crossref (52) Another advantage microflow correlated surface:volume ratio, improved heat mass transfer, possibility perform mass-transfer-limited efficiently [10Su Y. al.Photochemical accelerated reactors: basic concepts applications.Chem. Eur. J. 2014; 20: 10562-10589Crossref (328) Reactive chemicals intermediates can be handled safely as no accumulation dangerous components occurs within confined volume continuous nature process. Together, result faster, safer, higher-yielding reactions, under conditions impossible (high P/T; so-called novel process windows [11Hessel V. al.Novel enabling, accelerating, uplifting chemistry.ChemSusChem. 2013; 6: 746-789Crossref (439) Scholar]), make systems valid alternative traditional purposes. Moreover, ease automation coupling inline analysis, separation, purification multistep synthesis automated production platforms. These nicely showcased growing [12Bogdan A.R. Dombrowski A.W. Emerging trends applications industry.J. Med. 62: 6422-6468Crossref (65) 13Bogdan Organ M.G. drug discovery tool: medicinal perspective.in: Sharma U.K. Van der Eycken E.V. Chemistry Synthesis Heterocycles. 2018: 319-341Crossref 14Hughes D.L. Applications development: patent literature.Org. Process Res. Dev. 2018; 22: 13-20Crossref (51) 15May S.A. processing, manufacturing: perspective.J. 137-145Crossref (44) 16Bennett J.A. al.Role green manufacturing pharmaceuticals specialty chemicals.Curr. Opin. Eng. 26: 9-19Crossref (16) typical setup comprises transparent tubing perfluorinated materials PFA, ETFE) coiled around [17Hook B.D.A. al.A practical Org. 2005; 70: 7558-7564Crossref (290) Scholar], or surrounded it, 1E). expensive flat, microreactors engraved irradiated sides plate. In review, we present advances specific areas which compared chemistry. emerged cases complementary way reactions. Stephenson discusses complementarity between (thermal) fields cross-coupling alkene functionalization instance, first case, stubborn substrates thermal alkyl halides) employed conditions, limitations oxidative additions transmetalation steps overcome. industrial increasingly flow, shown Figures 3E, 4C, 5E ). functionalization, mechanisms become available photoredox, allowing broadening substrate scope.Figure 3Solar Photochemistry.Show full caption(A) Examples parabolic concentrators (left) flat-bed (right). Adapted, permission, [56Oelgemöller M. Solar synthesis: beginnings solar commodity chemicals.Chem. 9664-9682Crossref (135) (B) Luminescent concentrator-PhotoMicroreactor (LSC-PM) principle. [61Cambié leaf-inspired luminescent concentrator energy-efficient photochemistry.Angew. Int. Ed. 56: 1050-1054Crossref (73) 63Cambie al.Energy-efficient concentrator-based photomicroreactors.Angew. 58: 14374-14378Crossref (35) (C) Down-conversion 640-nm red LSC-PM. (D) Automated residence time adjustment according [63Cambie (E) Reactions simulator: comparison LSC-PM microchannel identical conditions. Scholar].View Large Image ViewerDownload (PPT)Figure 4Automated Screening Platforms Basic principle platforms via segmented flow. Beeler's platform multidimensional screening. [78Martin V.I. al.Multidimensional tool discovering new chemotypes.J. 79: 3838-3846Crossref (28) Jensen's oscillatory system study examples investigated. [79Hwang Y.-J. on-demand compound oscillating droplets.Chem. Commun. 53: 6649-6652Crossref 80Coley C.W. al.Material-efficient microfluidic exploratory studies catalysis.Angew. 9847-9850Crossref (25) 81Hsieh H.-W. iridium–nickel dual-catalyzed decarboxylative arylation cross-coupling: self-optimizing reactor.Org. 542-550Crossref (58) Noël's procedure quenching Stern–Volmer analysis. [82Kuijpers K.P.L. fluorescence analysis.Angew. 57: 11278-11282Crossref (33) 5Scale-Up Strategies Designs.Show Scale-up aglain three reactors series. [87Yueh H. scale syntheses rocaglate natural product analogues.Bioorg. 25: 6197-6202Crossref (19) Kilogram-scale trifluoromethylation arenes. [90Beatty J.W. perfluoroalkylation pyridine-N-oxides: mechanistic insights performance kilogram scale.Chem. 456-472Abstract (131) External numbering-up photoreaction. [92Su convenient strategy gas–liquid flow.React. 73-81Crossref Firefly reactor. [84Elliott L.D. small-footprint, high-capacity UV scale.Org. 1806-1811Crossref (78) AbbVie's kilogram-scale stirred-tank (CSTR)–laser setup. [96Harper K.C. laser driven scaling visible light.ACS Cent. 5: 109-115Crossref (69) (PPT) (A) also milder generate reactive otherwise obtained chemicals. An example generation singlet oxygen, commonly encountered benchmark (Figures 2A–D, 4C) wastewater treatment. other starting alkaline oxides hydrogen peroxide (dark oxygen); 2 mol reducing atom economy producing water, known quencher oxygen. Furthermore, might interfere reagents, requires often-toxic [18Wahlen al.Solid sources synthetically useful oxygen.Adv. Synth. Catal. 2004; 346: 152-164Crossref (106) comparison, intermediate catalytic amounts photocatalyst Radical another class investigated 2A 5B). trifluoromethyl radical alternatively generated variety reagents action stoichiometric oxidants reductants. hydroperoxides (superstoichiometric amounts), presence ca. 10% Fe Cu catalyst their activation. Alternatively, TEMPO derivatives have uncatalyzed While some protocols performed room temperature, atom-uneconomic Togni Umemoto used, several wasteful [19Studer A. "renaissance" trifluoromethylation.Angew. 2012; 51: 8950-8958Crossref (774) Gas cheaper, sustainable, atom-economic liquid solid alternatives therefore represent best option green-chemistry perspective. Gases are, however, difficult handle batch. Filling headspace gas unpressurized results serious limitations, while pressurized safety concerns case toxic gases, and/or require steel flasks autoclaves) that prevent Microflow represents better methods, it avoids high each section easily safe manner, providing good transfer large, well-defined interfacial without compromising [20Hone C.A. al.The molecular oxygen go?.ChemSusChem. 10: 32-41Crossref (71) 21Cantillo Kappe C.O. Halogenation compounds using microreactor technology.React. 2: 7-19Crossref 22Gemoets H.P.L. al.Liquid phase oxidation microreactors.Chem. Soc. 45: 83-117Crossref Several developed [23Mallia C.J. Baxendale I.R. gases synthesis.Org. 327-360Crossref (186) generally suitable It worth noting limits usable pressure range, relatively pressures tolerated tubing. Solid–liquid contrary, constant challenge feeding pumping manner not straightforward. Even initially where products formed clogging [24Hartman R.L. Managing solids upstream processing fine chemicals.Org. 16: 870-887Crossref (175) 25Lapkin A.A. al.Solids syntheses.in: Vaccaro L. Sustainable Chemistry. Wiley-VCH, 2017: 277-308Crossref (10) 26Horie al.Photodimerization maleic anhydride clogging.Org. 2010; 14: 405-410Crossref (141) tricks exist deal sonication [27Fernandez Rivas Kuhn S. Synergy microfluidics ultrasound.Top. Curr. 374: 70Crossref (48) trouble chemists. However, heterogeneous sustainable recycling, separation). Because this, effort expended towards transferring into few facilitate task. Segmented (Taylor slug flow) simplest method transformations, does any special equipment, widely approach. From pure feed, simple T/Y-shaped mixer required intercalated bubbles, contact surface two phases 2A). internal recirculation movement segments ensures mixing diffusion inside liquid. Many types employing strategy, including trifluoromethylations CF3I [28Straathof N.J.W. al.Practical photocatalytic hydrotrifluoromethylation styrenes flow.Angew. 55: 15549-15553Crossref (117) 29Straathof five-membered heterocycles flow.ChemSusChem. 1612-1617Crossref (115) C–H oxidations O2 [30Laudadio G. al.Selective C(sp3)−H aerobic enabled decatungstate photocatalysis 4078-4082Crossref (79) carboxylations CO2 [31Seo activation carbon dioxide amino acid flow.Nat. 453Crossref (181) 32Seo al.Direct β-selective hydrocarboxylation catalysis.J. Am. 139: 13969-13972Crossref (93) interesting antimalarial artemisinin photogenerated directly extracts plant Artemisia annua, containing precursor [dihydroartemisinic (DHAA)] chlorophyll photocatalyst, Gilmore [33Triemer al.Literally extracts.Angew. 5525-5528Crossref tube-in-tube (developed Ley [34Brzozowski al.Flow chemistry: intelligent reactor.Acc. 2015; 48: 349-362Crossref (187) Scholar]) comprising concentric tubes filled respectively solution separated gas-permeable membrane. permeates membrane diffuses homogeneously 2B). primarily presaturate prior [35Micic N. Polyzos carbonylation mediated photocatalysis: access 2,3-dihydrobenzofurans.Org. Lett. 4663-4666Crossref (21) 36de Souza J.M. al.Continuous endoperoxidation conjugated dienes subsequent rearrangements leading oxidized synthons.J. 83: 7574-7585Crossref 37Kouridaki Huvaere K. Singlet reactor.React. 590-597Crossref materials, applications, Park colleagues photooxygenation monoterpenes [38Park C.Y. monoterpenes.RSC Advances. 4233-4237Crossref Falling-film miniaturized adapted setup, injected top, forming thin layer (film), counterflow bottom, ensuring increased 2C). window falling-film rare, reported Oelgemöller Rehm [39Shvydkiv O. al.Visible-light α-terpinene falling film microreactor.Catal. Today. 308: 102-118Crossref (14) 40Rehm T.H. al.Photonic contacting light.React. 636-648Crossref interestingly, catalysis. was Rueping, who TiO2-catalyzed diazoarenes operating blue-light [41Fabry D.C. al.Blue heteroarenes TiO2 immobilized microreactor.Green 19: 1911-1918Crossref were coated catalyst, inert (rather

Язык: Английский

---

Luminescent First-Row Transition Metal Complexes

JACS Au, Год журнала: 2021, Номер 1(11), С. 1860 - 1876

Опубликована: Сен. 24, 2021

Precious and rare elements have traditionally dominated inorganic photophysics photochemistry, but now we are witnessing a paradigm shift toward cheaper more abundant metals. Even though emissive complexes based on selected first-row transition metals long been known, recent conceptual breakthroughs revealed that much broader range of in different oxidation states useable for this purpose. Coordination compounds V, Cr, Mn, Fe, Co, Ni, Cu show electronically excited with unexpected reactivity photoluminescence behavior. Aside from providing compact survey the key advances dynamic field, our Perspective identifies main design strategies enabled discovery fundamentally new types 3d-metal-based luminophores photosensitizers operating solution at room temperature.

Язык: Английский

---

Photoactive Copper Complexes: Properties and Applications

Chemical Reviews, Год журнала: 2022, Номер 122(22), С. 16365 - 16609

Опубликована: Ноя. 9, 2022

Photocatalyzed and photosensitized chemical processes have seen growing interest recently become among the most active areas of research, notably due to their applications in fields such as medicine, synthesis, material science or environmental chemistry. Among all homogeneous catalytic systems reported date, photoactive copper(I) complexes been shown be especially attractive, not only alternative noble metal complexes, extensively studied utilized recently. They are at core this review article which is divided into two main sections. The first one focuses on an exhaustive comprehensive overview structural, photophysical electrochemical properties mononuclear typical examples highlighting critical structural parameters impact being presented enlighten future design complexes. second section devoted application (photoredox catalysis organic reactions polymerization, hydrogen production, photoreduction carbon dioxide dye-sensitized solar cells), illustrating progression from early current state-of-the-art showcasing how some limitations can overcome with high versatility.

Язык: Английский

---

Recent progress in the development of transition-metal based photoredox catalysts

Coordination Chemistry Reviews, Год журнала: 2019, Номер 405, С. 213129 - 213129

Опубликована: Дек. 10, 2019

Язык: Английский

---

Cyclic (Amino)(aryl)carbenes Enter the Field of Chromophore Ligands: Expanded π System Leads to Unusually Deep Red Emitting Cu^I Compounds

Journal of the American Chemical Society, Год журнала: 2020, Номер 142(19), С. 8897 - 8909

Опубликована: Апрель 17, 2020

A series of copper(I) complexes bearing a cyclic (amino)(aryl)carbene (CAArC) ligand with various complex geometries have been investigated in great detail regard to their structural, electronic, and photophysical properties. Comparison [CuX(CAArC)] (X = Br (1), Cbz (2), acac (3), Ph2acac (4), Cp (5), Cp* (6)) known CuI (amino)(alkyl), monoamido, or diamido carbenes (CAAC, MAC, DAC, respectively) as chromophore ligands reveals that the expanded π-system CAArC leads relatively low energy absorption maxima between 350 550 nm THF high coefficients 5–15 × 103 M–1 cm–1 for 1–6. Furthermore, 1–5 show intense deep red near-IR emission involving triplet excited states solid state PMMA films λemmax 621–784 nm. Linear [Cu(Cbz)(DippCAArC)] (2) has found be an exceptional (λmax 621 nm, ϕ 0.32, τav 366 ns) thermally activated delayed fluorescence (TADF) emitter radiative rate constant kr ca. 9 105 s–1, exceeding those commercially employed IrIII- PtII-based emitters. Time-resolved transient upconversion experiments complemented by quantum chemical calculations employing Kohn–Sham density functional theory multireference configuration interaction methods well temperature-dependent steady-state time-resolved luminescence studies provide detailed picture excited-state dynamics 2. To demonstrate potential applicability this new class low-energy emitters future photonic applications, such nonclassical light sources communication cryptography, we successfully conducted single-molecule photon-correlation 2, showing distinct antibunching required single-photon

Язык: Английский

---