CS-[BiC-PiC]-NiCl4: a green and effective heterogeneous catalyst for one-pot synthesis of 2,3-dihydroquinazolin-4(1H)-one derivatives

Abstract

In this study, a novel nickel ion-containing dicationic ionic liquid immobilized on chitosan (CS-[BiC-PiC]-NiCl₄) was designed, synthesized, and fully characterized by using various techniques such as Fourier transform infrared spectroscopy (FT-IR), ¹H NMR and ¹³CNMR spectra, X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), and inductively coupled plasma (ICP) analysis. The theoretical electronic structure, catalytic mechanism, and identity of most of the active sites in the CS-[BiC-PiC]-NiCl₄ system were investigated using a suite of computational methods, including density functional theory (DFT), molecular electrostatic potential (MEP) mapping, quantum theory of atoms in molecules (QTAIM), and reduced density gradient (RDG) analysis. Its potential was demonstrated in the facile and eco-friendly synthesis of pharmacologically important 2,3-dihydroquinazolin-4(1H)-one derivatives using two distinct protocols, including the reaction of 2-aminobenzamide with aldehydes and the reaction of isatoic anhydride with ammonium acetate and aldehydes under neat conditions at 120 °C, demonstrating excellent recyclability over five runs, achieving high yields (93–97%) with short reaction times (3–8 minutes). This offers a sustainable and practical synthetic platform, facilitated by the synergistic interplay between the nickel Lewis acid sites and the chitosan support. This process provides significant advantages, including operational simplicity, solvent-free conditions, straightforward product isolation, and easy recovery of a cost-effective catalyst, which demonstrated exceptional stability over multiple cycles with no detectable nickel leaching, underscoring its truly heterogeneous nature. Consequently, this methodology represents a sustainable and practical approach for the synthesis of these valuable heterocycles.