Molecular catalysts for CO2/epoxide copolymerization to polycarbonates: From metal selection to performance benchmarks

The rising atmospheric CO 2 levels have intensified global efforts to mitigate climate change and limit its associated impacts. CO 2 utilization provides a sustainable route to value-added chemicals, fuels, and materials, and catalytic CO 2 /epoxide ring-opening copolymerization (ROCOP) to polycarbonates is among the most promising pathways. Recently, metal complexes have emerged as highly efficient molecular catalysts for polycarbonate synthesis, enabling tunable activity and polymer properties through metal choice, ligand design, cocatalyst/ion-pair engineering, and control over epoxide scope. This review surveys molecular catalysts based on cobalt(III), zinc(II), aluminum(III), chromium(III), iron(III), nickel(II), and magnesium(II) for CO 2 /epoxide ROCOP, with emphasis on recent advances. Particular attention is given to how the coordination environment, ligand structure, and cocatalyst interactions govern catalytic activity, selectivity, and polymer microstructure. A benchmarking approach is presented to enable comparison of catalysts across different metal families and operating conditions. Representative systems operate under 1–60 bar CO 2 and 20–120 °C, achieving TON values up to 55,000 and TOF up to 155,000 h −1 , with number-average molecular weights (M n ) up to 300 kg/mol. Hybrid strategies combining molecular and heterogeneous catalysis can further increase M n to ∼700 kg/mol. Finally, remaining challenges, including enhancing activity under mild conditions, suppressing by-product formation, and achieving precise control over polymer molecular weight and microstructure, are discussed. By identifying key coordination-chemistry relationships, this review provides guidelines for the rational design of next-generation catalysts for CO 2 -derived polycarbonates.