Synthesis, structural characterization, catalytic activity, and DFT studies of Cu(II) and Ni(II) Schiff base complexes for CO2 cycloaddition to cyclic carbonates
摘要
In this study, two novel Schiff base ligands (HA and HB) and their corresponding Cu(II) and Ni(II) complexes namely [Cu(A)2], [Ni(A)2], [Cu(B)2] and [Ni(B)2] were synthesized. The resulting compounds were comprehensively characterized using elemental analysis, Fourier-transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, molar conductivity measurements, and single-crystal X-ray diffraction. Density functional theory (DFT) calculations were performed at the B3LYP/6-311 + + G(d, p) level of theory to optimize molecular geometries, investigate keto-enol tautomerism, and evaluate the nonlinear optical (NLO) properties of the systems. Furthermore, the catalytic activity of the complexes was assessed for the solvent-free cycloaddition of carbon dioxide (CO2) with epoxides under high-pressure conditions. Among the catalysts tested, the [Ni(A)2]/DMAP system exhibited the highest performance and selectivity toward cyclic carbonate formation under optimized reaction conditions.