A sulfonic acid-functionalized amine-linked covalent organic framework as a robust catalyst for the preparation of pyrrole-2-ones.

In recent years, covalent organic frameworks (COFs) have emerged as powerful heterogeneous catalysts. Notwithstanding, attainment of both crystallinity and stability of COF-based catalysts under harsh conditions is still challenging. Herein, an imine-linked COF has been transformed into an amine-linked COF via the reduction of imine linkages. Amine linkages, due to their stable and irreversible nature, were functionalized with sulfonic acid groups, A-COF/SO3H, as a highly active catalytic center. X-ray diffraction (XRD) analysis clearly shows that the crystallinity of COF after modification was preserved. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analyses revealed that A-COF/SO3H has a plate-like intergrown morphology. The porosity of A-COF/SO3H was investigated by N2 adsorption/desorption, indicating a mesoporous structure with a surface area of 93 m2 g-1. To explore the catalytic performance, A-COF/SO3H was used as an acidic heterogeneous catalyst for the preparation of pyrrole-2-ones. Excellent yield of products, short reaction times and easy work-up are some of the major preferences of this protocol. Moreover, A-COF/SO3H exhibited good heterogeneity engineering potential and was recovered and reused up to four consecutive cycles without significant loss of its performance.