N-Heterocyclic Carbene Ag(I)–Based UiO-67 Metal-Organic Frameworks for the CO2 Conversion to Cyclic Carbonates under Mild Conditions

Abstract

The preparation of cyclic carbonate from CO₂ is one of the effective ways to utilize its resources. Herein, a series of N-heterocyclic carbenes (NHCs) Ag(I)–based UiO-67-type metal-organic frameworks (MOFs), UiO-bpdc-NHC/Ag, UiO-(bpdc-NH₂)-NHC/Ag, and UiO-(bpdc-F₃)-NHC/Ag are reported. These MOFs are characterized using powder X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and ¹⁹F NMR (nuclear magnetic resonance), confirming Ag(I) integration. Among them, due to the affinity of trifluorocarbonamide group for CO₂ and the high activity of NHC/Ag, UiO-(bpdc-F₃)-NHC/Ag possesses the best catalytic performance for the CO₂ conversion to cyclic carbonates. Notably, the catalyst exhibits robust activity under diluted CO₂ akin to flue gas, demonstrating high stability and recyclability. Mechanistic insights implicate Ag(I)-mediated polarization of propargylic alcohols’ CC bond, facilitating CO₂ insertion and ring-closure to α-alkylidene cyclic carbonates. This study underscores MOF-based catalysts’ potential in sustainable CO₂ utilization, offering a pathway for efficient chemical synthesis in environmentally sensitive contexts.