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.