Construction of Ultrastable Nonsubstituted Quinoline‐Bridged Covalent Organic Frameworks via Rhodium‐Catalyzed Dehydrogenative Annulation

Exploring new routes to lock the dynamic C=N bonds in imine‐linked covalent organic frameworks (COFs) is highly desired for enhancing their stability and functionality. Herein, a novel C=N bridge locking strategy via rhodium‐catalyzed [4+2] annulation is developed to construct nonsubstituted quinoline‐linked COFs (NQ‐COFs). The notable feature of this strategy includes high C=N conversion efficiency, oxidant‐free, and generality for synthesis of a variety of NQ‐COFs with high chemical stability. Particularly, after post‐synthetic modification, the crystallinity, topology, and porosity of pristine imine‐linked COFs are well retained. When used as photocatalysts, NQ‐COFs display better visible light absorption and carriers’ separation efficiency due to enhanced in‐plane π conjugation ability, as well as more facile generation of superoxide anion radicals than their counterparts, thus leading to efficient synthesis of 2,4,6‐tris(aryl)pyridines, benzimidazole, and sulfoxide derivatives. The oxidant‐free locking of a dynamic imine bridge to construct the ultrastable nonsubstituted quinoline‐linked COFs via rhodium‐catalyzed [4+2] annulation is reported. This methodology features high efficiency, generality, retention of crystallinity and topology. The enhanced in‐plane π‐conjugation facilitates photocatalytic organic transformations mediated by superoxide anion radicals.