Lai Yihuan, Halder Arjun, Kim Jaehwan, Hicks Thomas J, Milner Phillip J
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, 14853, USA.
Angew Chem Int Ed Engl. 2023 Oct 2;62(40):e202310246. doi: 10.1002/anie.202310246. Epub 2023 Aug 22.
Single-electron transfer (SET) plays a critical role in many chemical processes, from organic synthesis to environmental remediation. However, the selective reduction of inert substrates (E <-2 V vs Fc/Fc ), such as ubiquitous electron-neutral and electron-rich (hetero)aryl chlorides, remains a major challenge. Current approaches largely rely on catalyst photoexcitation to reach the necessary deeply reducing potentials or suffer from limited substrate scopes. Herein, we demonstrate that cumulenes-organic molecules with multiple consecutive double bonds-can function as catalytic redox mediators for the electroreductive radical borylation of (hetero)aryl chlorides at relatively mild cathodic potentials (approximately -1.9 V vs. Ag/AgCl) without the need for photoirradiation. Electrochemical, spectroscopic, and computational studies support that step-wise electron transfer from reduced cumulenes to electron-neutral chloroarenes is followed by thermodynamically favorable mesolytic cleavage of the aryl radical anion to generate the desired aryl radical intermediate. Our findings will guide the development of other sustainable, purely electroreductive radical transformations of inert molecules using organic redox mediators.
单电子转移（SET）在从有机合成到环境修复等许多化学过程中起着关键作用。然而，惰性底物（相对于Fc/Fc，E<-2 V）的选择性还原，如普遍存在的电子中性和富电子（杂）芳基氯化物，仍然是一个重大挑战。目前的方法主要依赖于催化剂光激发以达到必要的深度还原电位，或者底物范围有限。在此，我们证明了具有多个连续双键的累积烯烃有机分子可以作为催化氧化还原介质，用于在相对温和的阴极电位（相对于Ag/AgCl约-1.9 V）下对（杂）芳基氯化物进行电还原自由基硼化反应，而无需光照射。电化学、光谱和计算研究支持，从还原的累积烯烃到电子中性氯芳烃的逐步电子转移之后，芳基自由基阴离子发生热力学有利的均裂裂解，生成所需的芳基自由基中间体。我们的发现将指导使用有机氧化还原介质对惰性分子进行其他可持续的、纯电还原自由基转化反应的开发。
