Dinickel-Catalyzed N=N Coupling Reactions for the Synthesis of Hindered Azoarenes

Azoarenes are the largest class of photoswitching molecules, and they have a broad range of applications in photopharmacology and materials science. Azoarenes possessing ortho-substitution often display improved properties, including isomerization under visible light irradiation, near-quantitative switching, and long thermal half-lives in the cis form. The synthesis of hindered ortho-substituted azoarenes is often low-yielding using established oxidative or reductive coupling methods. Here, we describe the design and synthesis of a new dinickel complex that catalyzes the dimerization of ortho-substituted aryl azides in high yield. Applications of this method in the synthesis of high-performance photoswitches, photoactive peptide cross-linkers, hindered diazocines, and main-chain azoarene polymers are described.