Photochemical and Thermal Activation of a Diarylbismuth Azide

Azides are widely employed in synthesis as convenient nitrene precursors, particularly in transition-metal chemistry, where metal-nitrene intermediates enable diverse C─H amination, aziridination, and atom-transfer processes. In stark contrast, main-group azides, especially bismuth ones, are underrepresented and have not been fully exploited as nitrene sources. Herein, we report the synthesis and full characterization of a diarylbismuth monoazide supported by a diphenylsulfone-based dianionic ligand. The complex is robust toward air, moisture, and elevated temperatures, enabling detailed photochemical and chemical studies. Ultrafast UV-pump/mid-IR-probe spectroscopy demonstrates that 266 nm excitation triggers rapid azide-to-ligand charge transfer and loss of the azide antisymmetric stretching band. FTIR-monitored trapping with t-butyl isonitrile produces a new absorption band in the heterocumulene region, suggesting the formation of a nitrene intermediate. Alternatively, Lewis-acid activation with B(C₆F₅)₃ produces a stable adduct that undergoes thermal N₂ extrusion, transmetalation, and cycloaddition to form a tetrazaborole dimer. These divergent activation pathways establish bismuth azides as viable nitrene precursors and expand the reactivity landscape of heavy p-block chemistry.