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Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Isolation of a Highly Reactive CBNC Heterocumulene via Azidoborylene Photolysis: Facile Access to a Crystalline
Hayley King1, Vignesh Pattathil1, William Kennedy1
1Department of Chemistry, Charles E. Fipke Centre For Innovative Research, University of British Columbia-Okanagan Campus, Kelowna, BC, Canada.
Abstract:
Oxidation of the formal boron(0) complex MeCAAC2B in the presence of tetrabutylammonium azide leads to the formation of a formal boron(I) species bearing an N3 - anion-an azidoborylene. Irradiation of this complex with UV-C light results in the loss of N2 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.
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