Investigating Host–Guest Complexes in the Catalytic Synthesis of Cyclic Carbonates from Styrene Oxide and CO₂

Abstract

Combining tetraalkyl-ammonium halides and cavitand hosts as catalysts, we achieved the carboxylation of styrene oxide to produce cyclic styrene carbonate from CO2 in good to excellent yields. In a first approach and in the presence of tetraalkyl-ammonium chloride/tetraphosphonate cavitand catalytic systems, an enhanced activity of the catalytic reaction of styrene oxide was observed depending on the host–guest association. In a second set of experiments, using tetramethylammonium halide/tetraphosphonate cavitand complexes as catalysts, we obtained the corresponding styrene carbonate in high yields, whereas used alone, the tetramethylammonium salts are inactive under similar mild experimental conditions. The reaction involves the strong binding properties of the cavitand hosts toward ammonium salts. It is emphasized that the structure of the host–guest association is crucial. This simple protocol offers a new approach toward the synthesis of cyclic carbonates and provides the first example of a host–guest-catalyzed, metal-free, reaction for CO2 valorization.