CdS Quantum Dots as Potent Photoreductants for Organic Chemistry Enabled by Auger Processes

Journal of the American Chemical Society, Год журнала: 2022, Номер 144(27), С. 12229 - 12246

Опубликована: Июнь 30, 2022

Strong reducing agents (<−2.0 V vs saturated calomel electrode (SCE)) enable a wide array of useful organic chemistry, but suffer from variety limitations. Stoichiometric metallic reductants such as alkali metals and SmI2 are commonly employed for these reactions; however, considerations including expense, ease use, safety, waste generation limit the practicality methods. Recent approaches utilizing energy multiple photons or electron-primed photoredox catalysis have accessed reduction potentials equivalent to Li0 shown how this enables selective transformations aryl chlorides via radicals. However, in some cases, low stability catalytic intermediates can turnover numbers. Herein, we report ability CdS nanocrystal quantum dots (QDs) function strong photoreductants present evidence that highly electron is generated two consecutive photoexcitations QDs with intermediate reductive quenching. Mechanistic experiments suggest Auger recombination, photophysical phenomenon known occur photoexcited anionic QDs, generates transient thermally excited electrons observed reductions. Using blue light-emitting diodes (LEDs) sacrificial amine reductants, phosphate esters up −3.4 SCE photoreductively cleaved afford hydrodefunctionalized functionalized products. In contrast small-molecule catalysts, stable under conditions numbers 47 500 been achieved. These also effect other challenging reductions, tosylate protecting group removal amines, debenzylation benzyl-protected alcohols, ring opening cyclopropane carboxylic acid derivatives.

Язык: Английский

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Red Light-Based Dual Photoredox Strategy Resembling the Z-Scheme of Natural Photosynthesis

JACS Au, Год журнала: 2022, Номер 2(6), С. 1488 - 1503

Опубликована: Июнь 10, 2022

Photoredox catalysis typically relies on the use of single chromophores, whereas strategies, in which two different light absorbers are combined, rare. In photosystems I and II green plants, separate chromophores P680 P700 both absorb independently one another, then their excitation energy is combined so-called Z-scheme, to drive an overall reaction that thermodynamically very demanding. Here, we adapt this concept perform photoredox reactions organic substrates with input red photons instead blue or UV light. Specifically, a CuI bis(α-diimine) complex combination situ formed 9,10-dicyanoanthracenyl radical anion presence excess diisopropylethylamine catalyzes ca. 50 dehalogenation detosylation reactions. This dual approach seems useful because less damaging has greater penetration depth than radiation. UV-vis transient absorption spectroscopy reveals subtle change solvent from acetonitrile acetone induces changeover mechanism, involving either dominant photoinduced electron transfer triplet-triplet pathway. Our study illustrates mechanistic complexity systems operating under multiphotonic conditions, it provides insights into how competition between desirable unwanted steps can become more controllable.

Язык: Английский

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Formation and degradation of strongly reducing cyanoarene-based radical anions towards efficient radical anion-mediated photoredox catalysis

Nature Communications, Год журнала: 2023, Номер 14(1)

Опубликована: Янв. 6, 2023

Cyanoarene-based photocatalysts (PCs) have attracted significant interest owing to their superior catalytic performance for radical anion mediated photoredox catalysis. However, the factors affecting formation and degradation of cyanoarene-based PC (PC•‒) are still insufficiently understood. Herein, we therefore investigate PC•‒ under widely-used photoredox-mediated reaction conditions. By screening various PCs, elucidate strategies efficiently generate with adequate excited-state reduction potentials (Ered*) via supra-efficient generation long-lived triplet excited states (T1). To thoroughly behavior in actual reactions, a reductive dehalogenation is carried out as model identified dominant photodegradation pathways PC•‒. Dehalogenation coexistent depending on rate electron transfer (ET) substrate strongly depends electronic steric properties PCs. Based understanding both PC•‒, demonstrate that efficient highly reducing allows catalyzed aryl/alkyl halides at loading low 0.001 mol% high oxygen tolerance. The present work provides new insights into reactions reactions.

Язык: Английский

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Mechanochemical Approach for Air‐Tolerant and Extremely Fast Lithium‐Based Birch Reductions in Minutes

Angewandte Chemie International Edition, Год журнала: 2023, Номер 62(21)

Опубликована: Март 22, 2023

Birch reduction has been widely used in organic synthesis for over half a century as powerful method to dearomatize arenes into 1,4-cyclohexadiene derivatives. However, the conventional reaction using liquid ammonia requires laborious procedures ensure inert conditions and low temperatures. Although several ammonia-free modifications have reported, development of an operationally simple, efficient, scalable protocol remains challenge. Herein, we report lithium-based air without special operating ball-milling technique. This is characterized by its operational simplicity extremely short time (within 1 min), probably owing situ mechanical activation lithium metal, broad substrate scope, no requirement dry bulk solvents. The potential our flash also demonstrated efficient bioactive target molecules gram-scale synthesis.

Язык: Английский

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Visible-light-driven synthesis of N-heteroaromatic carboxylic acids by thiolate-catalysed carboxylation of C(sp²)–H bonds using CO2

Nature Synthesis, Год журнала: 2024, Номер 3(3), С. 394 - 405

Опубликована: Янв. 11, 2024

Язык: Английский

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Excited Organic Radicals in Photoredox Catalysis

JACS Au, Год журнала: 2025, Номер 5(2), С. 426 - 447

Опубликована: Янв. 29, 2025

Many important synthetic-oriented works have proposed excited organic radicals as photoactive species, yet mechanistic studies raised doubts about whether they can truly function photocatalysts. This skepticism originates from the formation of (photo)redox-active degradation products and picosecond decay electronically radicals, which is considered too short for diffusion-based photoinduced electron transfer reactions. From this perspective, we analyze synthetic transformations where been photocatalysts, comparing their theoretical maximum state potentials with required observed photocatalytic reactivity. We summarize structurally similar photocatalysts indicating different reaction pathways some catalytic systems, addressing cases radical exceed Additionally, perform a kinetic analysis to explain in on subpicosecond time scales. further rationalize potential anti-Kasha reactivity higher states femtosecond lifetimes, highlighting how future photocatalysis advancements could unlock new photochemical pathways.

Язык: Английский

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Excited State Anions in Organic Transformations

Angewandte Chemie International Edition, Год журнала: 2020, Номер 60(12), С. 6270 - 6292

Опубликована: Окт. 1, 2020

Utilizing light is a smart way to fuel chemical transformations as it allows the energy be selectively focused on certain molecules. Many reactions involving electronically excited species proceed via open-shell intermediates, which offer novel and unique routes expand hitherto used synthetic toolbox in organic chemistry. The direct conversion of non-prefunctionalized, less activated compounds highly desirable goal pave towards more sustainable atom-economic processes. Photoexcited closed-shell anions have been shown reach extreme potentials single electron transfer reveal unusual excited-state reactivity. It is, therefore, surprising that their use reagent or photocatalyst limited few examples. In this Review, we briefly discuss characteristics anionic photochemistry, highlight pioneering work, show recent progress has made by utilizing photoexcited synthesis.

Язык: Английский

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Electro‐mediated PhotoRedox Catalysis for Selective C(sp³)–O Cleavages of Phosphinated Alcohols to Carbanions

Angewandte Chemie International Edition, Год журнала: 2021, Номер 60(38), С. 20817 - 20825

Опубликована: Июнь 24, 2021

We report a novel example of electro-mediated photoredox catalysis (e-PRC) in the reductive cleavage C(sp

Язык: Английский

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Scalable Birch reduction with lithium and ethylenediamine in tetrahydrofuran

Science, Год журнала: 2021, Номер 374(6568), С. 741 - 746

Опубликована: Ноя. 4, 2021

The Birch reduction dearomatizes arenes into 1,4-cyclohexadienes. Despite substantial efforts devoted to avoiding ammonia and cryogenic conditions, the traditional, cumbersome, dangerous procedure remains standard. Benkeser with lithium in ethylenediamine converts a mixture of cyclohexenes cyclohexanes; this is operationally easier than but does not afford Here, we report promoted by (or analogs) tetrahydrofuran at ambient temperature. Our method easy set up, inexpensive, scalable, rapid, accessible any chemical laboratory, capable reducing both electron-rich electron-deficient substrates. protocol also compatible organocuprate chemistry for further functionalization.

Язык: Английский

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Electrochemical Activation of Diverse Conventional Photoredox Catalysts Induces Potent Photoreductant Activity**

Angewandte Chemie International Edition, Год журнала: 2021, Номер 60(39), С. 21418 - 21425

Опубликована: Июль 20, 2021

Herein, we disclose that electrochemical stimulation induces new photocatalytic activity from a range of structurally diverse conventional photocatalysts. These studies uncover electron-primed photoredox catalyst capable promoting the reductive cleavage strong C(sp2 )-N and )-O bonds. We illustrate several examples synthetic utility these deeply reducing but otherwise safe mild catalytic conditions. Finally, employ current measurements to perform reaction progress kinetic analysis. This technique reveals improved this system is consequence an enhanced stability profile.

Язык: Английский

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