Basic ionic liquid anchored on UiO-66-NH2 metal-organic framework: a stable and efficient heterogeneous catalyst for synthesis of xanthenes

In this study, the Zr-based metal-organic framework, UiO-66-NH2, was modified with ionic liquid (dibutylimidazolium bromide) to generate a platform for supporting an organocatalyst of guanidine. After an anion exchange, the prepared hybrid system was denoted as UiO-66-NH2-ILPF6--guanidine. The catalyst was characterized by different techniques such as PXRD, FTIR, TEM, SEM-EDS, TGA, and BET. The basic heterogeneous catalyst was then utilized for the synthesis of xanthene derivatives via a reaction of aldehydes with dimedone. Various types of aromatic aldehydes were employed for the synthesis with medium to high yield. The study of catalytic activities showed that the heterogenization of guanidine significantly promotes catalytic performance in comparison with guanidine in a homogeneous form. The heterogeneous catalyst is stable in the reaction medium and can be recycled for at least four times without significant reduction in activity. The stability of the catalyst was also investigated by XRD, FTIR, SEM/elemental mapping, and leaching test.