This review highlights the evolution of catalysts for coupling carbon dioxide and epoxides to form polycarbonates and cyclic carbonates. It critically compares homogeneous and heterogeneous systems and concludes with recent progress in metal-free organocatalysts as promising sustainable alternatives for CO₂ utilization.

Abstract

The selective synthesis of polycarbonates (PCs) or cyclic carbonates via catalytic conversion of epoxides and carbon dioxide (CO₂) is an efficient pathway for producing valuable products from CO₂. This approach has received significant attention because it offers control over mechanical, thermal, and degradable characteristics of the resulting PCs. However, activating CO₂ as a C1-feedstock in such reactions is a challenging task owing to the considerable thermodynamic stability of CO₂. Therefore, the use of catalysts along with precise temperature and pressure control is essential for successful CO₂ copolymerization with cyclic ethers. Since Inoue and co-workers pioneering discovery of zinc-based catalysts for these reactions in 1969, substantial advancements have been made for understanding the mechanisms of these catalytic systems. These developments have led to the synthesis of more efficient catalytic systems that can operate under ambient conditions and allow selective epoxides/CO₂ copolymerization. Metal-based catalytic systems, particularly those utilizing Zn, Co, Cr, and Al have dominated this field, while recent reports highlight the potential of metal-free organocatalytic systems. Alongside specific catalytic frameworks, many novel molecules have been introduced into the catalytic toolbox. This review will summarize recent developments in exploring novel catalysts for the catalytic conversion of CO₂ and epoxides into aliphatic polycarbonates.