Cr(iii)-salophen catalysts: efficient single-component and binary systems for sustainable CO2/cyclohexene oxide copolymerization

Abstract

The rise in carbon dioxide (CO₂) emissions and the accumulation of human-made CO₂ in the atmosphere are recognized as the primary causes of the greenhouse effect. Therefore, one strategy to address this issue is capturing and utilizing CO₂ as a raw material for producing high-value chemical compounds. The most promising reactions involve the catalytic conversion of CO₂ with epoxides to produce polycarbonates (PC). For this purpose, Co(III) and Cr(III) complexes (Cat1–Cat9) with salophen-type ligands were synthesized and tested as catalysts for the copolymerization of cyclohexene oxide (CHO) with CO₂ to create poly(cyclohexene)carbonate (PCHC). Their catalytic activity was initially assessed in single-component systems at 100 °C and 8 bar of CO₂ for 24 hours, where Cat5 demonstrated the highest selectivity. Subsequent optimization studies explored the effect of solvents, CO₂ pressure, and co-ligand variation. The best performance was obtained with the Cat5:DMAP binary system, producing a semi-crystalline PCHC copolymer with a high degree of isotacticity.