Unwinding Antiaromaticity in 1-Bromo-2,3,4,5-tetraphenylborole

Borole systems tend to undergo various reactions driven by the disruption of its destabilizing antiaromatic character. As a consequence, the isolation and characterization of free boroles is challenging, especially when the substituents around the C4B framework are sterically less demanding. In the present paper we report the synthesis of 1-bromo-2,3,4,5-tetraphenylborole. The title compound readily undergoes a dimerization/rearrangement reaction in analogy to the previously reported 1-chloro-2,3,4,5-tetraphenyborole to form an isostructural product identified by X-ray crystallography. Additionally we present the formation of Lewis acid-base adducts of the title compound with 3,5-lutidine, PCy3, N-hetrocyclic carbene, cyclic (amino) (alkyl)carbene, and THE. The latter compounds were analyzed by single-crystal X-ray diffraction and compared.