The generation of highly reducing electrons to drive reductive chemistry is an important tool in organic synthesis. Stoichiometric metallic reductants such as alkali metals and SmI<sub>2</sub> are commonly employed for their extreme reducing power, while recent approaches have employed energy from multiple photons or photoelectrochemistry to catalytically generate electrons as reducing as Li<sup>0</sup>. Herein we disclose the ability of CdS Quantum Dots to function as strong photoreductants, and present mechanstic studies suggesting that two consecutive photoexcitations of CdS QDs with intermediate reductive quenching generate an excited electron with the energy of both absorbed photons to perform challenging reductions. We postulate that this process occurs via Auger recombination, a photophysical phenomenon known to occur in photoexcited anionic QDs, which generates transient hot electrons to enable the observed reductions. Using blue LEDs and sacrificial amine reductants, aryl chlorides with reduction potentials up to -3.4 V vs. SCE are efficiently hydrodechlorinated as a model reaction. Other chemistry applications will also be discussed.

Auger recombination enables challenging reductions by photoexcited anionic CdS quantum dots

ACS Fall 2021

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