A spiroborate-based anionic bis-N-heterocyclic carbene.

A twisted mono-cationic bis-benzimidazolium salt was serendipitously isolated from the dehydrative condensation of 5,6-dihydroxyl-1,3-dimesityl-benzimidazolium and 1,4-benzenediboronic acid. Subsequent deprotonation of the benzimidazolium salt led to the formation of a spiroborate-linked free bis-NHC, which was further transformed into the corresponding diborane adduct and the di-Rh complex.