Transformation of carbon dioxide catalyzed using an N-heterocyclic carbene copper(i)-embedded metal–organic framework†

Transformation of carbon dioxide (CO₂) into high-value chemicals has attracted increasing attention because CO₂ is an abundant, inexpensive and non-toxic renewable carbon resource. Herein, a novel three-dimensional metal–organic framework, namely, {[Zn₄(μ₄-O)(L)₄·4(H₂O)]·2(NO₃)}_n (Zn-MOF), was synthesized under hydrothermal conditions using an azolium-based ligand, 1,3-bis(4-carboxybenzyl)-4-methyl-1H imidazolium chloride (H₂L⁺Cl⁻). Subsequently, Cu(I)-NHC@Zn-MOF was prepared by introducing N-heterocyclic carbine-Cu(I) active sites into the Zn-MOF using a post-synthesis modification (PSM) method, and it was characterized through powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and inductively coupled plasma optical emission spectroscopy (ICP-OES). Cu(I)-NHC@Zn-MOF was successfully employed as a highly efficient catalyst for the C–H activated carboxylation of terminal alkynes with CO₂ (1 atm) under mild conditions, achieving an isolated yield of up to 98%. The catalyst exhibited excellent recyclability and maintained high activity over three consecutive cycles without losing its structural integrity. Additionally, the role of Cu(I)-NHC@Zn-MOF and the reaction mechanism were comprehensively discussed.