Structurally Diverse Boron–Nitrogen Heterocycles from an N2O23? Formazanate Ligand

Five new compounds comprised of unprecedented boron–nitrogen heterocycles have been isolated from a single reaction of a potentially tetradentate N₂O₂^3? formazanate ligand with BF₃?OEt₂ and NEt₃. Optimized yields for each product were obtained through variation of experimental conditions and rationalized in terms of relative Gibbs free energies of the products as determined by electronic structure calculations. Chemical reduction of two of these compounds resulted in the formation of a stable anion, radical anion, and diradical dianion. Structural and electronic properties of this new family of redox-active heterocycles were characterized using UV/vis absorption spectroscopy, cyclic voltammetry and X-ray crystallography.