Single-Site Bifunctional Catalysts for COX (X = O or S)/Epoxides Copolymerization: Combining High Activity, Selectivity, and Durability

Unprecedented activity (TOF > 270 000 h –1 ), high polymer selectivity (>99%), and excellent durability (TON > 600 000) were observed in the copolymerization of carbonyl sulfide (COS) and epoxides mediated by the single-site bifunctional chromium catalyst containing a Lewis acidic metal center and a sterically hindered organic base in a molecule, selectively producing the corresponding poly(thiocarbonate)s with completely alternating structure, high molecular weight, and narrow monodispersity. No oxygen–sulfur exchange reaction occurred even at an elevated temperature of 80 °C. Nevertheless, this catalyst was not efficient for CO 2 /epoxides copolymerization. The presence of CO 2 completely inhibits the reactivity of COS. Contrarily, the corresponding Co(III) complex with the same ligand showed very low activity for COS/epoxides copolymerization but excellent activity (TOF > 13 000 h –1 ) for CO 2 /epoxides copolymerization at both ambient and high temperatures, affording the polycarbonates with >99% carbonate linkages and high molecular weight up to 467.0 kg/mol.