Diborabutatriene: an electron deficient cumulene

The complexation of two equivalents of a cyclic (amino)alkylcarbene (CAAC) to tetrabromodiborane(4), followed by reduction with four equivalents of sodium naphthalide led to the formation of the CAAC-stabilized linear diboracumulene (CAAC)2B2. The capacity of the CAAC ligand to facilitate B2?CAAC donation of p-electron density resulted in important differences between this species and a previously reported complex featuring a B=B triple-bond stabilized by cyclic di(amino)carbenes, including a longer B–B bond and shorter B–C bonds. Frontier orbital analysis indicated sharing of valence electrons across the entire linear C–B–B–C unit in (CAAC)2B2, which is supported by natural population analysis and cyclic voltammetry.