Zn-salen complexes with multiple hydrogen bonding donor and protic ammonium bromide: Bifunctional catalysts for CO2 fixation with epoxides at atmospheric pressure

Bifunctional Zn-salen complexes with multiple hydrogen bonding donors and protic ammonium bromides were developed as efficient catalysts for the formation of 4-phenyl-1,3-dioxolan-2-one from styrene oxide and CO 2 . Owing to synergistic effects of multiple sites on epoxide activation (Lewis acidic zinc, phenolic hydroxyl group and protonated tertiary ammonium able to activate epoxide and bromide anion acting as a nucleophile), the easily-synthesized Zn-salen complexes showed outstanding performance at mild reaction conditions (CO 2 0.1   MPa, 100   °C) using only 0.3   mol% catalyst amount. Besides, this protocol is applicable to a variety of epoxides including internal epoxide, giving the corresponding cyclic carbonates in good to excellent yields. Notably, 200   mmol-scale experiment was successfully conducted and TON of 49288   ±   13 and TOF of 39473   ±   8   h −1 were achieved.