Carbon Dioxide Activation and Conversion by Hyperbranched Polyethylenimine/ZnI2 Catalysts

The combination from hyperbranched polyethylenimine and Lewis acid ZnI2 (PEI/ZnI2) was facilely obtained, and they showed an efficient activity to the reaction of epoxides and CO2 because of these abundant primary, secondary, and tertiary amines of PEI; additionally, ZnI2 made contribution to the activation of epoxide. With 0.15 g PEI-4 (MW 70 000) and the molar percentage of 2.0 mmol % ZnI2 to propylene oxide (PO), 95% yield was achieved at 100 °C, 3.0 h, and 1.0 MPa, and the selectivity was 96%. Moreover, the PEI-4 catalyst preparation avoided toxic solvents and the harsh preparation conditions. Furthermore, PEI-4/ZnI2 was easily recycled from the entire system. The catalytic system maintained excellent recyclability up to eight times with satisfactory activity, and thus, the facile and efficient PEI-4/ZnI2 catalysts were considered as an industrial candidate for the reaction of epoxides and CO2 to cyclic carbonates.