Visible Light Photoredox Catalyzed Biaryl Synthesis Using Nitrogen Heterocycles as Promoter

Although transition-metal-catalyzed direct arylation of aromatic C-H bonds is one of the most efficient ways for the construction of biaryl targets, it is also expected for other alternative methods that can use inexpensive catalysts and abundant solar energy to drive chemical reactions. Herein, we describe a new activation mode for biaryl synthesis by using a photosensitive complex of potassium tert-butoxide (KOt-Bu) and nitrogenous heterocyclic ligands via visible light excitation. Under low-energy visible light irradiation, the single-electron transfer from electron-donor KOt-Bu to electron-deficient nitrogenous heterocycle occurred in the inner part of the complex by using potassium as a bridge atom. The ligand accepted the as-photoexcited single electron and transformed into stable radical anions which played a dominant role in the coupling reactions of benzene with aryl halides at ambient temperature. This reaction paradigm features the use of inexpensive catalyst, abundant visible light energy, and more accessible bromobenzene for the construction of biaryl compounds under rather mild conditions.