Embedding Hydrogen Atom Transfer Moieties in Covalent Organic Frameworks for Efficient Photocatalytic C−H Functionalization

Abstract

AbstractCovalent organic frameworks (COFs) have emerged as efficient heterogeneous photocatalysts for a wide range of relatively simple organic reactions, whereas their application in complex organic transformations, like site‐selective functionalization of unactivated C−H bonds, is underexplored, which can be mainly attributed to the lack of highly active organophotocatalytic cores. Herein through bonding oxygen atoms at the N‐terminus of quinolines in nonsubstituted quinoline‐linked COFs (NQ−COFs), we successfully realized the embedding of active hydrogen atom transfer (HAT) moieties into the skeleton of COFs. This novel designed COF (NQ−COFE5−O), serving as both an excellent photosensitizer and HAT catalyst, exhibited much higher efficiency in C−H functionalization than the corresponding NQ−COFE5. Specially, we evaluated the photocatalytic performance of NQ−COFE5−O on ten different substrates, including quinolines, benzothiazole, and benzoxazole, all of which were transferred to desired products in moderate to high yields (up to 93 %). Furthermore, the as‐synthesized NQ−COFE5−O displayed excellent photostability and could be reused with negligible loss of activity for five catalytic cycles.