Engineering Nb2O5 embedded quinoline-linked COF as a high-performance catalyst for synthesis of tetrahydropyridines and α-aminobenzyl-4-hydroxycoumarins

Abstract

Recently, the development of metal oxide embedded covalent organic frameworks (COFs) for promoting their chemical and physical properties, is taken into consideration. In the current study, we investigate synthesis of metal oxide-COF hybrid namely QCOF@Nb₂O₅, via post synthetic decoration of a quinoline-linked COF by Nb₂O₅. Thanks to the presence of carboxylic acid groups in the structure of QCOF and due to the presence of hydroxyl groups in the surface of Nb₂O₅, these lead to successful decoration of Nb₂O₅ on the surface and pores of QCOF. After post modification, the morphology, chemical and physical properties of QCOF are affected by Nb₂O₅. The co-existence of the Nb₂O₅ particles, acidic functional groups, and acceptable specific surface area, significantly increased the catalytic activity of QCOF-Nb₂O₅ towards the multicomponent preparation of tetrahydropyridines and α-aminobenzyl-4-hydroxycoumarins with (70–98 % yields). Meanwhile, the convenient functional group tolerance and high yields of derivatives are highlighted benefits for the catalytic preparation of these chemicals.