Trapping of a Borirane Intermediate in the Reductive Coupling of an Arylborane to a Diborene.
Alexander HermannMerle ArrowsmithDaniel E Trujillo-GonzalezJosé Oscar Carlos Jimenez-HallaAlfredo VargasHolger BraunschweigPublished in: Journal of the American Chemical Society (2020)
The reductive coupling of a N-heterocyclic carbene (NHC)-stabilized aryldibromoborane yields a mixture of trans- and cis-diborenes in which the aryl groups are coplanar with the diborene core. Under dilute reduction conditions two diastereomers of a borirane-borane intermediate are isolated, which upon further reduction give rise to the aforementioned diborene mixture. DFT calculations suggest a mechanism proceeding via nucleophilic attack of a dicoordinate borylene intermediate on the aryl ring and subsequent intramolecular B-B bond formation.