To establish the optimal reaction conditions, we first focused on studying the effect of the solvent and halide salt on the reaction yield and in the absence of MMOs. Thus, the reaction of CO2 with styrene oxide 1a to give the corresponding cyclic carbonate 2a was investigated. Tetrabutylammonium iodide (TBAI) and potassium iodide were used as the halide salts at concentrations of 10 and 100 mol%, respectively, and ethanol and acetonitrile were used as the solvents. Better yields were obtained with ethanol (Table , entries 2-5) than with acetonitrile (Table and). With no halide salt present, the reaction did not proceed with either solvent (Table , entries 1 and 6). With ethanol as the solvent and 10 mol% TBAI or KI, cyclic carbonates were obtained in good yields (Table , entries 2 and 4). The yield decreased when the reaction was carried out in acetonitrile and 10 mol% TBAI or KI (Table and). The maximum yield is achieved when the reaction is carried out with one equivalent of halide salt (Table and). The use of TBAI or KI is decisive for the opening of the epoxide and the formation of halohydrin anion, which is a key intermediate in the catalytic process as previously demonstrated. The complete kinetics of the reactions are shown in the SI.