Heterodinuclear Co(III)Na(I) Catalysts for the Ring-Opening Copolymerization of Propene Oxide and Carbon Dioxide.

The ring-opening copolymerization of propene oxide and carbon dioxide is an effective route to make polycarbonates. Catalysts showing high activities, high polymer selectivities, molecular weight control, and tolerance to impurities are rare. Here, a series of four Co-(III)-Na-(I) catalysts are tested for the ring-opening copolymerization of propene oxide and carbon dioxide. The complexes have systematic variations in the ligand structure in which both Co-(III) and Na-(I) binding sites are modified. Significant differences in catalyst performance are observed, with the lead catalyst featuring six oxygen donors and an ethylene diamine linker. This catalyst shows excellent activity and high poly-(propene carbonate) selectivity at elevated temperatures (TOF = 1428 h-1, poly-(propene carbonate) selectivity = 98%, 20 bar CO2, 70 °C), outperforming analogous Co-(III)-K-(I) catalysts. These results inform on the optimal coordination environment and operating conditions for the Co-(III)-Na-(I) catalysts and highlight the benefits of using Na-(I) relative to heavier s-block metals in the heterodinuclear catalysts.