Pd/Cu bimetallic catalyst immobilized on PEI capped cellulose-polyamidoamine dendrimer: Synthesis, characterization, and application in Sonogashira reactions for the synthesis of alkynes and benzofurans

Abstract

Polyamidoamine dendrimer (PAMAM) is an efficient material for immobilization of Pd(II) complex due to its unique tree-like structure and properties. To the purpose of enhancing of the loading of Cu(II) ions, a polyethyleneimine end-capped microcrystalline cellulose-polyamidoamine dendrimer (G2.5) (MCC-PAMAMG2.5-PEI) was designed and synthetized. The resultant MCC-PAMAMG2.5-PEI was furtherly treated by PdCl2 and CuSO4 solution to afford the corresponding dendrimer-supported Pd/Cu bimetallic catalyst (Pd/Cu@MCC-PAMAMG2.5-PEI). As a result, both Pd(II) and Cu(II) ions were well selectively immobilized within the interior architectures and exterior PEI layers of dendrimers, respectively. The as-prepared catalyst was fully characterized by elemental analysis (EA), inductively coupled plasma atomic emission spectrometry (ICP-AES), Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), elemental mappings, energy-dispersive X-ray spectra (EDX), field emission transmission electron microscopy (FETEM), and thermogravimetry analysis (TGA) techniques. The presence of required Pd and Cu elements were confirmed from ICP-AES, XPS, EDX, and elemental mappings analysis, respectively. The synergetic effect between Pd and Cu can be observed by comparing it to the dendrimer supported monometallic Pd and Cu as well as the mixture of dendrimer supported Pd and Cu. The catalyst showed excellent performance in the synthesis of alkynes and benzofurans via Sonogashira reactions and could be reused for seven successive runs without any noteworthy loss of activity. Moreover, its efficiency was compared with other reported catalysts in the same transformations.