Efficient fixation of CO2 with epoxides catalyzed by Mg(II)-N4 complexes

Abstract

In this study, a series of Mg(II) complexes supported by aminopyridine-N4 (MEP, DAP, TPA) and TMC (14-TMC) ligands were synthesized and characterized using various spectroscopic techniques. These Mg(II) complexes were investigated the catalytic activity for the cycloaddition of carbon dioxide with epoxides to obtain cyclic carbonates under cocatalyst- and solvent-free conditions, providing moderate to excellent yields depending on the specific N4 ligands used. The study involved analyzing the spectroscopic characterizations and experimental results to discuss the possible ligand topological structures of Mg-N4 complexes and their impact on catalytic performance. Moreover, the addition of (triphenylphosphoranylidene)ammonium chloride (PPNCl) as a cocatalyst significantly enhanced the turnover frequency (TOF) to 2100 h^-1 for the Mg-1 [MEP-Mg(II), 0.01 mol % catalyst loading]. Also, the Mg-1 catalyst demonstrates excellent stability under the reaction conditions, allowing for multiple reuses.