Copper Incorporated Covalent Organic Framework as a Heterogeneous Catalyst for CuAAC Reaction

Abstract Covalent organic frameworks (COFs) incorporating metal are attractive alternatives for metal‐catalyzed organic transformations. For effective metal incorporation in COF a favorable ligand environment is required. Pyridine and hydrazone units can provide effective binding sites for transition metals. The major challenge in synthesizing hydrazone‐linked COFs is the inherent flexibility of the linker, causing differences in lengths and orientations during solvothermal synthesis. We demonstrate that incorporation of enol form in the framework facilitates non‐covalent interactions such as hydrogen bonding, reduces degrees of freedom and enhances rigidity. Here, we synthesized TFP‐PyHz COF utilizing 2,4,6‐trihydroxybenzene‐1,3,5‐tricarbaldehyde (TFP) and pyridine‐2,6‐dicarbohydrazide. Enol form in the framework was confirmed by comparing the IR and 13 C solid‐state NMR spectra of TFP‐PyHz with its model compound. The presence of this enol form also facilitates the incorporation of Cu 2+ through post‐modification as confirmed by IR and XPS analysis of postmodified Cu‐TFP‐PyHz. The copper‐incorporated material Cu‐TFP‐PyHz is utilized as a heterogeneous catalyst for copper‐catalyzed click reactions, enabling the synthesis of 1,4‐triazoles.