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.