Dinickel-Catalyzed\nN=N Coupling Reactions for the\nSynthesis of Hindered Azoarenes

Azoarenes are the largest class of\nphotoswitching molecules,\nand\nthey have a broad range of applications in photopharmacology and materials\nscience. Azoarenes possessing <i>ortho</i>-substitution\noften display improved properties, including isomerization under visible\nlight irradiation, near-quantitative switching, and long thermal half-lives\nin the <i>cis</i> form. The synthesis of hindered <i>ortho</i>-substituted azoarenes is often low-yielding using\nestablished oxidative or reductive coupling methods. Here, we describe\nthe design and synthesis of a new dinickel complex that catalyzes\nthe dimerization of <i>ortho</i>-substituted aryl azides\nin high yield. Applications of this method in the synthesis of high-performance\nphotoswitches, photoactive peptide cross-linkers, hindered diazocines,\nand main-chain azoarene polymers are described.