Isolation of a Highly Reactive CBNC Heterocumulene via Azidoborylene Photolysis: Facile Access to a Crystalline Dioxaborirane

ABSTRACT Oxidation of the formal boron(0) complex Me CAAC 2 B in the presence of tetrabutylammonium azide leads to the formation of a formal boron(I) species bearing an N 3 − anion—an azidoborylene. Irradiation of this complex with UV‐C light results in the loss of N 2 and the selective formation of a reactive C═B═N═C heterocumulene. Electronic structure analysis reveals strong multiple bonding in this species, and reactivity studies indicate pronounced ambiphilicity at the boron center. This complex was found to exhibit unprecedented reactivity within the realm of cumulenes including the scission of dihydrogen, the insertion of nitrile into the B═C bond forming an extended CCNBNC π‐conjugated system, as well as the activation of dioxygen to form a three‐membered ─B─O─O─ ring—a dioxaborirane. Plausible mechanisms for each transformation have been elucidated via DFT calculations, which have indicated a triplet Criegee intermediate in the formation of the dioxaborirane that rapidly cyclizes upon spin‐crossover.