Immobilization of Ag and Pd over a novel amide based covalent organic framework (COF-BASU2) as a heterogeneous reusable catalyst to reduce nitroarenes

Reducing nitroarenes to their amines is among the common and vital reactions with remarkable industrial significance. This study describes an eco-friendly recyclable catalyst for reducing nitroarene. For this purpose, a new strategy was designed to synthesize a new amide-based COF through the reaction between 1,4‑diaminobenzene and trimesic acid (BTC). In this synthesis pathway, BTC is activated with carbonyl diimidazole (CDI), followed by its reaction with 1,4-diaminobenzene. Eventually, the desired COF (i.e., COF-BASU2) is synthesized. Next, it is decorated via silver (Ag) and palladium (Pd) ions to synthesize Ag/COF-BASU2 and Pd/COF-BASU2. The as-synthesized materials are properly characterized through ICP-OES, TG-DTA, FT-IR, EDX, XRD, TEM, and N2 isotherms. The simulation results have suggested a multi layers of two dimensional frameworks of COF-BASU2. Furthermore, Ag and Pb ions have shown to be placed on the surface and between the layers of COF, respectively. Then, we used molecular hydrogen as a reducing agent to investigate the Pd/COF-BASU2′s catalytic activity for nitroaromatic hydrogenation with excellent chemoselectivity and wide scope. In addition, NaBH4 was used as a reductant along with Ag/COF-BASU2 to reduce the nitro group on electronically diversified nitroarenes selectively. The remarkable characteristics of this catalytic system are the great turnover number (TON), considerably high selectivity, good turnover frequency (TOF), high yield, fast and almost complete conversion of nitrobenzene to the desired aniline, and facile and convenient segregation of catalyst and product. According to the obtained results, using Ag/COF-BASU2 offers the highest yields in the shortest reaction time.