Engineering of Phenylpyridine- and Bipyridine-Based Covalent Organic Frameworks for Photocatalytic Tandem Aerobic Oxidation/Povarov Cyclization
Maarten Debruyne, Sander Borgmans, Sambhu Radhakrishnan, Eric Breynaert, Henk Vrielinck, Karen Leus, Andreas Laemont, Juul S. De Vos, Kuber Singh Rawat, Siebe Vanlommel, Hannes Rijckaert, Hadi Salemi, Jonas Everaert, Flore Vanden Bussche, Dirk Poelman, Rino Morent, Nathalie De Geyter, Pascal Van Der Voort, Véronique Van Speybroeck, Christian V. Stevens
Abstract
Covalent organic frameworks (COFs) are emerging as a new class of photoactive organic semiconductors, which possess crystalline ordered structures and high surface areas. COFs can be tailor-made toward specific (photocatalytic) applications, and the size and position of their band gaps can be tuned by the choice of building blocks and linkages. However, many types of building blocks are still unexplored as photocatalytic moieties and the scope of reactions photocatalyzed by COFs remains quite limited. In this work, we report the synthesis and application of two bipyridine- or phenylpyridine-based COFs: TpBpyCOF and TpPpyCOF . Due to their good photocatalytic properties, both materials were applied as metal-free photocatalysts for the tandem aerobic oxidation/Povarov cyclization and α-oxidation of N -aryl glycine derivatives, with the bipyridine-based TpBpyCOF exhibiting the highest activity. By expanding the range of reactions that can be photocatalyzed by COFs, this work paves the way toward the more widespread application of COFs as metal-free heterogeneous photocatalysts as a convenient alternative for commonly used homogeneous (metal-based) photocatalysts.