Postsynthetic ionization of an imidazole-containing metal–organic framework for the cycloaddition of carbon dioxide and epoxides

Abstract

A bifunctional imidazolium functionalized zirconium metal-organic framework (Zr-MOF), (I^-)Meim-UiO-66 (<b>2</b>), was successfully prepared from the imidazole-containing Zr-MOF Im-UiO-66 (<b>1</b>) by a post-synthetic modification (PSM) method. It was found that the crystal size and pore features of the imidazole-containing <b>1</b> could be tuned at the nanoscale. The bifunctional MOF <b>2</b>, containing Brønsted acid sites and iodide ions, was shown to be an efficient and recyclable heterogeneous catalyst for the cycloaddition of carbon dioxide (CO₂) with epoxides, without the use of any co-catalyst, at ambient pressure. The solvent-free synthesis of the cyclic carbonate from CO₂ and an epoxide was monitored by <i>in situ</i> Fourier transform infrared spectroscopy (FT-IR) and an acid/base synergistic catalysis mechanism was proposed. We hope that our strategy provides an effective approach for the introduction of functional <i>N</i>-heterocyclic groups into MOFs for potential applications.