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.