Quantifying CO<sub>2</sub> 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
Abstract
High Resolution Image Download MS PowerPoint Slide While outstanding catalysts are known for the ring-opening copolymerization (ROCOP) of CO 2 and propene oxide (PO), few are reported at low CO 2 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% CO 2 ) and is highly effective at low pressures (<10 bar). CO 2 insertion is a prerate determining chemical equilibrium step. At low pressures, the concentration of the active catalyst depends on CO 2 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 CO 2 equilibrium constants estimated, showing that this unified rate law applies to other systems.