Noncrystalline Zeolitic Imidazolate Frameworks Tethered with Ionic Liquids as Catalysts for CO2 Conversion into Cyclic Carbonates.

Abstract

Noncrystalline zeolitic imidazolate frameworks (ZIFs) tethered with ionic liquids (ILs) were successfully employed as catalysts for mild CO2 conversion into cyclic carbonates for the first time. Notably, noncrystalline ZIFs exhibit outstanding catalytic performance in terms of activity, stability, and substrate suitability. Z3 was obtained through the simultaneous incorporation of a boronic acid group and ILs into its ZIF framework and exhibited a superior catalytic activity. A reaction mechanism for the propylene oxide-CO2 cycloaddition has been proposed, which integrates experimental findings with density functional theory calculations. The results indicate that zinc, ILs, and boronic acid play crucial roles in achieving high activity. Zinc and ILs are identified as key contributors to epoxide activation and ring opening, while boronic acid plays a crucial role in stabilizing the turnover frequency-determining transition states. The simplicity of this ZIF synthesis approach, combined with the high activity, stability, and versatility of the products, facilitates practical and efficient conversion of CO2 and epoxides into cyclic carbonates.