The Use of Sustainable Transition Metals for the Cycloaddition of Epoxides and CO₂ under Mild Reaction Conditions

Abstract

Following green chemistry principles, we present a one pot synthesis of zinc curcumin complex as a homogeneous, sustainable catalyst for cyclic carbonate (CC) synthesis from CO 2 and a variety of terminal and internal epoxides under 1 bar CO 2 at 60 °C using DMSO as a solvent. Zinc curcumin (Zn-Cur) complex was identified via 1 H/ 13 C NMR and ATR-FTIR spectroscopies, elemental analysis, ionic conductivity, and quantitative silver nitrate test to confirm a 1 : 1 molar ratio of metal to the ligand. Interestingly, Zn-Cur showed an outstanding perform-ance in catalysing the synthesis of renewable CCs including dimeric pinene and limonene carbonates. In this context, other metal complexes, including magnesium (Mg II ), calcium (Ca II ), and nickel (Ni II ) complexes showed good to excellent catalytic activity. Furthermore, a plausible reaction mechanism was investigated by density functional theory (DFT) calculations. The reaction was found to be overall exergonic by 39 kJ/mol and the rate determining step was CO 2 insertion, which is in good agreement with the experimental findings.