Role of Intralayer Hydrogen Bonding in the Fast Crystallization of the Hydrazone-Linked Nanoporous Covalent Organic Framework for Catalytic Suzuki–Miyaura Cross-Coupling Reactions

Covalent organic frameworks (COFs) are the emerging smart materials that can be designed and synthesized by tuning their structural diversity and topology for various applications. Despite vast advancements in the design of COFs, the synthetic methodologies to construct COFs are always a significant challenge. Herein, we demonstrate a fast crystallization in hydrazone-based Bth-Tp-COF, synthesized via a Schiff-base reaction between benzene-1,3,5-tricarbohydrazide (Bth) and triformylphloroglucinol (Tp) linkers under stirred conditions. The growth of the COF was typically completed in 30 min and likely driven by intra- and interlayer hydrogen bonding in COF layers, leading to the fast crystallization. Here, the intralayer hydrogen bonding prevented in-plane bond rotation, while the interlayer hydrogen bonding provided rigidity to the COF layers favoring the antiparallel stacking model. The synthesized Bth-Tp-COF was found to be highly stable in harsh chemicals such as 12 M HCl, 12 M NaOH, TFA, and water for 5 days. Moreover, when we doped palladium (Pd) in Bth-Tp-COF, the resulting Pd/Bth-Tp-COF was found to be a highly efficient heterogeneous catalyst for the Suzuki–Miyaura cross-coupling reaction that completed in a quick reaction time of only 20 min with excellent yields. In addition, Pd/Bth-Tp-COF displayed high activity in the recycling experiment with a slight decrease in its crystallinity up to five catalytic cycles. The fast crystallization and metal doping strategy in COFs open up several opportunities to develop excellent heterogeneous catalysts for various chemical transformations.