9‑Aza-10-boraanthracene Stabilized by Coordination of an N‑Heterocyclic Carbene and Its Methylated Cation: Synthesis, Structure, and Electronic Properties

9-Aza-10-boraanthracene stabilized by coordination of an N-heterocyclic carbene was synthesized. The X-ray crystallographic analysis disclosed a planar structure of the 9-aza-10-boraanthracene ring. The theoretical calculation and UV–vis absorption spectrum revealed a narrow HOMO–LUMO gap of 9-aza-10-boraanthracene. In addition, a nucleophilic reactivity of the lone pair of nitrogen atom in 9-aza-10-boraanthrcene was demonstrated by a reaction with MeOTf. The electronic structure of the N-methylated 9-aza-10-boraanthracene cation was also discussed on the basis of X-ray crystallographic analysis and its UV–vis absorption spectrum as well as theoretical calculations.