Pd-Isatin-Schiff base complex supported on graphene oxide as a catalyst for the Sonogashira cross-coupling reaction

Abstract

The study reports on the synthesis and characterization of palladium-Isatin-Schiff base complex supported on graphene oxide (Pd-Isatin-Schiff base@rGO), as well as its application in the Sonogashira cross-coupling reaction. The catalyst was easily prepared by a simple method through modification of GO with (3-aminopropyl) triethoxysilane (APTES) as a linker. The reaction of free amine groups with isatin allowed the synthesis of Isatin-Schiff base@rGO. The subsequent complexation/immobilization of palladium provided the Pd-Isatin-Schiff base@rGO nanocomposite with a Pd(II) to Pd(0) ratio=1.17. The prepared Pd-Isatin-Schiff base@rGO nanocomposite was fully characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), CHN elemental analysis, scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), thermogravimetric analysis (TGA), high-resolution transmission electron microscope (HRTEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectroscopy (ICP-OES) to establish its structure and composition. This heterogeneous nanocomposite catalyst was found very efficient for the cross-coupling reaction of an alkyne and an aryl halide, generating a high yield of coupling products (80–95 %) after 1 h. A reusability study revealed that the Pd-Isatin-Schiff base@rGO composite could be recycled for six consequent cycles without significant loss of its activity. However, after six cycles, the yield of 1,2-diphenylethyne as the coupling product decreased slightly from 93 % to 85 % and a decrease 8 wt.% in the Pd content was observed using ICP analysis.