Isolation and Reactivity of a Silylene-Stabilized Borasilylidene

The field of reactive carbenes and their heavier analogs has experienced extraordinary advancements in recent years. Among these, unsaturated variants have long been synthetic targets due to their unique electronic structures and reactivity profiles. However, their highly reactive nature poses significant challenges for isolation and characterization in the condensed phase. Here, we present the synthesis and characterization of a silylene-stabilized borasilylidene, a previously elusive unsaturated silylene featuring a B═Si double bond and a lone pair on silicon. This compound is capable of forming a unique π-complex with CuBr. Moreover, the borasilylidene displays exceptional cooperative reactivity toward B–F and C≡O bonds, leading to the formation of a silylene-stabilized diborylsilylene and a silylene-stabilized σ 0 π 2 (boryl)(silyneyl)carbene, respectively. The discovery of this species not only enhances our understanding of boryl-substituted unsaturated silylenes but also opens new avenues for their application in small-molecule activation.