Catalytic Non-redox Carbon Dioxide Fixation in Cyclic Carbonates

If cycloaddition of CO2 to epoxides is to become a viable non-redox CO2 fixation path, it is crucial that researchers develop an active, stable, selective, metal-free, reusable, and cost-effective catalyst. To this end, we report here a new catalyst that is based on imidazolinium functionality and is synthesized from an unprecedented, one-pot reaction of the widely available monomers terephthalaldehyde and ammonium chloride. We show that this covalent organic polymer (COP)-222 exhibits quantitative conversion and selectivity for a range of substrates under ambient conditions and without the need for co-catalysts, metals, solvent, or pressure. COP-222 is recyclable and has been demonstrated to retain complete retention of activity for over 15 cycles. Moreover, it is scalable to at least a kilogram scale. We determined the reaction mechanism by using quantum mechanics (density functional theory), showing that it involves nucleophilic-attack-driven epoxide ring opening (ND-ERO). This contrasts with the commonly assumed mechanism involving the concerted addition of chemisorbed CO2. To stop global warming, we must introduce a variety of CO2 reuse pathways. Redox chemistry is not trivial; reduction of CO2 back to methane requires up to 8 electrons per molecule, leading to heavy energy demand. Non-redox paths have low energy needs and could provide a quick relief. A promising non-redox CO2 product, cyclic carbonate is a versatile building block for green plastics and solvents. Although studies date back as early as 1969, no industrially viable process has since been introduced, mainly because of the lack of an effective catalyst for direct addition of CO2 to the epoxides. Conceptually, the ideal catalyst should (1) be free of metals; (2) be free of co-catalysts; (3) be free of high pressure requirements; (4) provide quantitative selectivity to cyclic carbonate (5) provide a wide substrate scope, including very hard substrates; (6) provide reusability; and (7) be inexpensive. The imidazolinium catalyst that we developed herein addresses all 7 qualities and offers rapid implementation for CO2 reclamation. Yavuz and colleagues introduced a highly active catalyst for non-redox fixation of CO2 into cyclic carbonates, a versatile product family with potential use in green polymers and solvents. The metal-free, heterogeneous imidazolinium network structure is easily made, scaled up, recycled, and inexpensive and provides quantitative selectivity and conversion yields over a wide substrate scope of epoxides.