Metal–organic frameworks with Lewis acid-base sites as highly efficient catalyst for the cycloaddition of carbon dioxide

The chemical fixation of carbon dioxide (CO2) into high value-added chemicals like cyclic carbonates is an effective strategy to solve the energy and ecological issues. Metal-organic frameworks (MOFs) can efficiently catalyze the reaction due to their diverse structures and accessible active sites, herein, two novel MOFs have been successfully constructed based on bi-functional ligand 4-(2, 4-dicarboxylphenyl)-4, 2': 6′, 4″-terpyridine) (H2dcptpy). The Fourier-transform infrared (FT-IR) spectra data indicated complete de-protonation of the H2dcptpy ligand, their structures have been refined and formulated as [Co(dcptpy)]∙DMF∙6H2O (MOF 1) with a large BET surface areas of 3.4 m2/g and [Cu(dcptpy)(H2O)2] (MOF 2). They both exhibit a three-dimensional network structure with microporosity and contain Lewis acid-base sites located on the surface of the pores. The good purity and stability of the as-synthesized samples were adequately characterized by powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA). Remarkably, a series of cycloaddition reactions of epoxides with CO2 show that MOF 1 has excellent heterogeneous catalytic activity for cyclic carbonate of epibromohydrin and butyl glycidyl ether, and almost complete conversion can be achieved even under mild conditions (1 bar CO2, 80 °C, 12 h and solvent-free). Therefore, MOF 1 has the potential to be a catalyst material for CO2 conversion.