Copper (II)‐azo sulfathiazole complex immobilized on UiO‐66‐NH2 (MOF) as a catalyst for the one‐pot synthesis of spiroindole‐pyranopyrazoles

Abstract

In this work, a new metal–organic framework nanocatalyst (Cu@UIO‐66‐AST) has been prepared from UiO‐66‐NH2 through a post‐synthesis modification process. The Cu (II)@UIO‐66‐AST nanocatalyst formation was confirmed from TGA, FT‐IR, TEM, XRD, BET, CHN, ICP, SEM, EDS, and elemental analyses. The catalytic efficiency of the synthesized MOF (Cu@UIO‐66‐AST), as an acid Lewis, was investigated in the four‐component reaction of isatin, malononitrile, hydrazine, and dimethyl acetylene dicarboxylate and compared to UiO‐66‐NH2 (as a basic catalyst) and Cu (OAc)2 (as an acidic heterogeneous catalyst). The obtained results clearly show that Cu@UIO‐66‐AST has a higher catalytic activity (93%) than UiO‐66‐NH2 (13%) and Cu (OAc)2 (43%). It could be due to the increase of dispersibility of Cu2+ by the formation of several stable complexes between Cu2+ ions and functional groups of ligand AST (OH, C=N, NH, and C‐S) on the surface of the nanocatalyst. Also, the catalyst can be recycled and reused for up to eight subsequent runs without significant loss of activity.