Photocatalysis with Quantum Dots and Visible Light: Selective and Efficient Oxidation of Alcohols to Carbonyl Compounds through a Radical Relay Process in Water

Abstract

Selective oxidation of alcohols to aldehydes/ketones has been achieved with the help of 3-mercaptopropionic acid (MPA)-capped CdSe quantum dot (MPA-CdSe QD) and visible light. Visible-light-prompted electron-transfer reaction initiates the oxidation. The thiyl radical generated from the thiolate anion adsorbed on a CdSe QD plays a key role by abstracting the hydrogen atom from the C-H bond of the alcohol (R CH(OH)R ). The reaction shows high efficiency, good functional group tolerance, and high site-selectivity in polyhydroxy compounds. The generality and selectivity reported here offer a new opportunity for further applications of QDs in organic transformations.

Light‐Driven Single‐Electron Transfer Processes as an Enabling Principle in Sulfur and Selenium Multicatalysis

“…Wu et al. reported in the same year a conceptually related approach toward the acceptorless dehydrogenation of alcohols using CdSe quantum dots (CDs) as photocatalysts in conjunction with adsorbed 3‐mercaptopropionic acid (MPA) and NiCl 2 , with the last two serving as a HAT catalyst and a catalytic proton reductant, respectively . In previous investigations, the same research group had shown that MPA‐capped CDs release thiyl radicals from the surface upon irradiation with visible light .…”

Lichtgetriebene Ein‐Elektronen‐Transferprozesse als Funktionsprinzip in der Schwefel‐ und Selen‐Multikatalyse

“…Wu et al. berichteten im selben Jahr über das zweite Beispiel einer akzeptorlosen Dehydrierung, wobei in diesem Fall primäre und sekundäre Alkohole 88 mittels eines katalytischen Systems bestehend aus 3‐Mercaptopropionsäure (MPS; auf CdSe‐Quantenpunkten adsorbiert vorliegend) und NiCl 2 zu den entsprechenden Carbonylverbindungen 90 oxidiert wurden. Hierbei übernehmen das Thiol und die Ni II ‐Spezies die Funktion eines HAT‐Katalysators bzw.…”

“…[53] Dieses Szenario wird auch durch Berichte über artverwandte Dimerisierungsreaktionen von Chalkogen-Radikalkationen gestützt. [55] [56] Deoxygenierungen [57] und Dehydrierungen, [58]…”

Photocatalysis with Quantum Dots and Visible Light for Effective Organic Synthesis

“…The fact that the generated thiyl radicals coupled before being able to diffuse into the solution implies that the thiyl radicals′ desorption from the surface of QDs is very slow. Taking advantage of these results, Wu and co‐workers intercepted the thiyl radical generated on the surface of the QDs photocatalysts with benzyl alcohols containing abstractable C−H hydrogen atoms, to achieve the selective and efficient oxidation of alcohols to carbonyl compounds through the thiyl radical relay process (Scheme ) . When benzyl alcohol was subjected to oxidation with MPA‐capped CdSe QDs as catalyst and with visible light as the energy source, it was quantitatively transformed to benzaldehyde with evolution of a stoichiometric amount of hydrogen.…”

“…Ta king advantage of these results, Wu and co-workersi ntercepted the thiyl radical generated on the surfaceo ft he QDs photocatalysts with benzyla lcohols containing abstractable CÀ Hh ydrogen atoms, to achieve the selectivea nd efficient oxidation of alcohols to carbonyl compoundst hrough the thiyl radical relay process( Scheme 2). [23] When benzyl alcoholw as subjected to oxidation with MPA-cappedC dSe QDsa sc atalyst and with visible light as the energy source, it was quantitatively transformed to benzaldehyde with evolutiono fastoichiometric amount of hydrogen. The generality of reactionw as established by investigating over two-dozen substituted benzyl alcohols, heterocyclic substituted alcohols, and a-alkylated benzyla lcohols.…”