Photochemical and Thermal Activation of a Diarylbismuth Azide

ABSTRACT

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(C ₆ F ₅ ) ₃ produces a stable adduct that undergoes thermal N ₂ 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.