Ortho-Functionalization of Azobenzenes via Hypervalent Iodine Reagents

Ortho-functionalized azobenzenes are much sought after molecular switches. They may be turned to absorb in the visible range of light and in many cases, the Z-isomer have very high thermal half-lives. However, methods to introduce substituents in ortho-position are still rare. This work presents the synthesis of azobenzenes with an iodine(III) moiety in the ortho-position. This novel class of diaryliodonium salts is demonstrated to efficiencly arylate oxygen, nitrogen, carbon and sulfur nucleophiles under metal-free conditions. Selective transfer of the azobenzene moiety to the nucleophile gives access to an unprecendented range of ortho-substituted azobenzenes. In addition, the structure of these versatile reagents has been analyzed by X-ray crystallography and their photo-switching properties were investigated by NMR and UV-vis spectroscopy.