AbstractSingle‐electron transfer (SET) plays a critical role in many chemical processes, from organic synthesis to environmental remediation. However, the selective reduction of inert substrates (Ep/2<−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.
摘要单电子转移(SET)在从有机合成到环境修复的许多化学过程中发挥着关键作用。然而,选择性还原惰性底物(Ep/2<-2 V vs Fc/Fc+),如无处不在的电子中性和电子丰富的(杂)芳基氯化物,仍然是一项重大挑战。目前的方法主要依赖催化剂的光激发来达到必要的深度还原电位,或者受限于底物范围。在此,我们证明了积雪烯--具有多个连续双键的有机分子--可以作为催化氧化还原介质,在相对温和的阴极电位(相对于 Ag/AgCl 约为 -1.9 V)下催化(杂)芳基氯的电还原自由基硼烷基化,而无需光辐射。电化学、光谱和计算研究证明,电子从还原型积雪烯逐步转移到电子中性的氯烯烃后,芳基自由基阴离子会发生热力学上有利的介解裂解,生成所需的芳基自由基中间体。我们的发现将为利用有机氧化还原介质对惰性分子进行其他可持续的纯电导自由基转化提供指导。