Pd immobilized on amidoxime-functionalized Mesoporous SBA-15: A novel and highly active heterogeneous catalyst for Suzuki–Miyaura coupling reactions

Abstract

Herein we described the synthesis of a novel SBA-15/AO/Pd(II) nanocatalyst by grafting of amidoxime on SBA-15 and subsequent deposition of palladium chlorides. Prior to grafting of amidoxime (AO), the prepared [2-cyanoethyl]-functionalized Mesoporous SBA-15 through combining of 2-cyanoethyltriethoxysilane and SBA-15 was treated with hydroxylamine. The amidoxime grafted SBA-15 (SBA-15/AO) were then used as platform for in situ deposition of Pd complex. The materials were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), inductivity coupled plasma (ICP), nitrogen adsorption–desorption, and Fourier transform infrared (FTIR) spectroscopy. SBA-15/AO/Pd(II) are novel phosphine-free recyclable heterogeneous catalyst for Suzuki coupling reaction of aryl halides (I, Br, Cl) with phenylboronic acid to provide the corresponding products. These cross-coupled products were produced in excellent yields under mild conditions at extremely low palladium loading (∼0.2mol%) with perfect high turnover frequencies (TOFs). The heterogeneous catalyst can be readily recovered by simple filtration and reused six times with loss in its activity.