Dynamic Imine Exchange Enables Access to Nanoporous Covalent Organic Frameworks with High Crystallinity for the Heck Reaction

Two-dimensional covalent organic frameworks (2D COFs) represent a useful class of porous crystalline materials with promising applications. However, the lack of a facile and general approach for the construction of highly crystalline COFs with desirable structures and functionalities still hinders their practical applications. Herein, we report a dynamic imine exchange strategy for fabricating nanoporous COFs with high crystallinity by using aryl-protected imines as building blocks. Two 2D COFs (i.e., COF-TD-Cl and COF-TP-Cl) with a higher yield and larger specific surface area were synthesized as compared with their counterparts prepared by direct condensation. Given its high crystallinity and good stability, COF-TD-Cl was further coordinated with palladium(II) trifluoroacetate through postsynthetic modification. The as-synthesized Pd/COF-TD-Cl exhibited remarkable catalytic activity as a heterogeneous catalyst for the Heck cross-coupling reaction and could be recycled up to ten times without significant loss of activity. This contribution not only provides an effective strategy to produce nanoporous COFs with high crystallinity but also extends the potential applications of COF-based composites in heterogeneous catalysis.