Grafting Schiff base Cu(II) complex on magnetic graphene oxide as an efficient recyclable catalyst for the synthesis of 4H-pyrano[2,3-b]pyridine-3-carboxylate derivatives

Abstract

Schiff base Cu(II) complex (Sc–Cu) stabilized on the surface of graphene oxide modified magnetic nanoparticles (GO/Fe3O4) using 3-chloropropyltrimethoxysilane ((MeO)3Si-PrCl) as a linker, (GO/Fe3O4@SPSc-Cu), was prepared, characterized and used as a magnetically separable and reusable heterogeneous catalyst in the multi-component reaction of aldehyde, 3-cyano-6-hydroxy-4-methyl-pyridine-2(1H)-one, and ethyl acetoacetate to afford a series of novel 4H-pyrano[2,3-b]pyridine-3-carboxylate derivatives under solvent-free conditions. The structure of the catalyst (GO/Fe3O4@SPSc-Cu) was characterized by Fourier-transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), elemental mapping, transmission electron microscopy (TEM), high resolution TEM (HRTEM), fast Fourier transform (FFT), scanning TEM (STEM), X-ray diffraction (XRD), thermogravimetry/derivative thermogravimetry (TG/DTG), and vibrating sample magnetometer (VSM) analyses. Various spectral analyses such as 1H and 13C NMR, FT-IR and ESI-MS were used to determine the structure of the products. The catalyst demonstrated good to excellent catalytic efficiency for reactions under green conditions using a wide range of substrates. The advantages of this process include a simple reaction set-up, high yield, short reaction time, environmentally friendliness, recyclable catalyst and easy separation of the products. In addition, the catalyst was recovered through magnetic decantation and reused for five consecutive cycles.