Quantifying CO2 Insertion Equilibria for Low-Pressure Propene Oxide and Carbon Dioxide Ring Opening Copolymerization Catalysts

Katharina H S Eisenhardt; Francesca Fiorentini; Wouter Lindeboom; Charlotte K Williams

doi:10.1021/jacs.3c13959

Quantifying CO₂ Insertion Equilibria for Low-Pressure Propene Oxide and Carbon Dioxide Ring Opening Copolymerization Catalysts

J Am Chem Soc. 2024 Apr 17;146(15):10451-10464. doi: 10.1021/jacs.3c13959. Epub 2024 Apr 8.

Authors

Katharina H S Eisenhardt¹, Francesca Fiorentini¹, Wouter Lindeboom¹, Charlotte K Williams¹

Affiliation

¹ Department Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford OX1 3TA, U.K.

Abstract

While outstanding catalysts are known for the ring-opening copolymerization (ROCOP) of CO₂ and propene oxide (PO), few are reported at low CO₂ pressure. Here, a new series of Co(III)M(I) heterodinuclear catalysts are compared. The Co(III)K(I) complex shows the best activity (TOF = 1728 h^-1) and selectivity (>90% polymer, >99% CO₂) and is highly effective at low pressures (<10 bar). CO₂ insertion is a prerate determining chemical equilibrium step. At low pressures, the concentration of the active catalyst depends on CO₂ pressure; above 12 bar, its concentration is saturated, and rates are independent of pressure, allowing the equilibrium constant to be quantified for the first time (K_eq = 1.27 M^-1). A unified rate law, applicable under all operating conditions, is presented. As proof of potential, published data for leading literature catalysts are reinterpreted and the CO₂ equilibrium constants estimated, showing that this unified rate law applies to other systems.