Electroreductive Borylation of Unactivated (Hetero)Aryl Chlorides Without Light Using Cumulene Electrocatalysts

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 (Ep/2 < −2 V vs Fc/Fc+), such as ubiqui-tous electron-neutral and electron-rich (hetero)aryl chlorides, remains a major challenge. Current catalytic approaches largely rely on light to reach the necessary deeply reducing potentials. A purely electrochemical approach would offer advantages in terms of reduced energy use, minimized waste, complementary selectivity, and improved scalability. Here-in, we demonstrate that cumulenes—organic molecules with multiple consecutive double bonds—can function as cata-lytic redox mediators for the first electroreductive borylation of (hetero)aryl chlorides under mild conditions without the need for photoirradiation. Electrochemical, spectroscopic, and computational studies support that electron transfer from reduced cumulene intermediates to electron-neutral chloroarenes is followed by highly favorable mesolytic cleavage of the aryl radical anion to generate the desired aryl radical intermediate. Our findings enable the development of other sus-tainable electroreductive transformations of inert molecules, complementing existing approaches that rely on photoexci-tation.