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 CO2. 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 (CO2 0.1 MPa, 100 degrees 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 1 13 and TOF of 39473 +/- 8 h(-1) were achieved. (C) 2016 Elsevier B.V. All rights reserved.