Triazine-based robust covalent organic framework enabled hydrogen-bond donor catalysis for the synthesis of highly substituted imidazole and pyrazole scaffolds

Abstract

Covalent organic frameworks (COFs), particularly triazine-based hydrogen-bond-donor COFs, have emerged as a promising class of porous and crystalline materials in the field of heterogeneous catalysis owing to their high surface areas, well-defined and tunable pore architectures, and excellent thermal and chemical stability. Furthermore, the abundance of hydrogen-bond donor sites within these frameworks promotes noncovalent interactions, i.e, hydrogen bonding, facilitating efficient catalytic transformations. These features play a crucial role in enhancing substrate activation and promoting a broad range of organic transformations. In this work, a novel triazine-based hydrogen-bond-donor covalent organic framework (HBD-COF) was synthesized and employed as a highly efficient heterogeneous catalyst for the synthesis of imidazole and pyrazole derivatives; the reactions proceeded under mild conditions and afforded the target products in excellent yields exceeding 90 % within 1.5 h. The (HBD-COF) was extensively characterised by FTIR, PXRD, BET, TGA, FE-SEM, EDS, HR-TEM, 13C CP/MAS NMR, and XPS. The above characterizations confirmed the highly ordered, porous architecture and chemical robustness of the material. Notably, the catalyst exhibited excellent recyclability, retaining both its catalytic efficiency and structural integrity over eight consecutive reaction cycles without significant loss of activity, as confirmed by the FTIR, PXRD, BET, TGA, FE-SEM, and EDS of the reused sample. These findings highlight the triazine-based HBD-COF as a stable, reusable, and high-performance catalytic platform for sustainable organic transformations.