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 13C solid-state NMR spectra of TFP-PyHz with its model compound. The presence of this enol form also facilitates the incorporation of Cu2+ 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.