Functionalization of graphene oxide with a hybrid P, N ligand for immobilizing and stabilizing economical and non-toxic nanosized CuO: an efficient, robust and reusable catalyst for the C–O coupling reaction in O-arylation of phenol

Abstract

Herein, we report a promising graphene oxide (GO) anchored robust and thermally stable heterogeneous catalytic system containing the low cost and less toxic copper oxide as a catalytically active material for C–O coupling reactions. A hybrid ligand (i.e. PPh₂–CH₂–CH₂–NH₂) has been used for the first time for functionalization of the GO surface. This ligand grafted over GO sheets via covalent linkages acts as an efficient stabilizing and chelating agent for CuO nanoparticles through P and N donor sites to form the catalytic system (GO–PN–CuO). The powder X-ray diffraction (PXRD), infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) studies, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and Raman spectroscopy confirmed the step-wise formation of GO–PN–CuO. The catalytic potential of GO–PN–CuO has been explored for the C–O coupling reactions of phenols with several aryl bromides and chlorides under mild reaction conditions. The covalent linkage of the hybrid ligand with GO sheets and the strong binding abilities of P, N donor sites with CuO render high stability to GO–PN–CuO. As a result, the catalytic system offers the advantage of recyclability up to five reaction cycles without any considerable loss in activity.