Nanochannel-based {BaZn}–organic framework for catalytic activity on the cycloaddition reaction of epoxides with CO2 and deacetalization-Knoevenagel condensation

Abstract

Herein, the rare combination of Ba^II (5s) and Zn^II (3d) in the presence of the structure-oriented TDP⁶⁻ ligand generated the nanochannel-based hybrid material {[(CH₃)₂NH₂]₂[BaZn(TDP)(H₂O)]·DMF·5H₂O}_n (NUC-51, H₆TDP = 2,4,6-tri(2,4-dicarboxyphenyl)pyridine), which possesses excellent physicochemical characteristics such as nanoscopic channels, high porosity, large specific surface area, and high heat/water-resistance. To the best of our knowledge, this is the first 3D [Ba^IIZn^II(CO₂)₆(H₂O)]-based nano-porous host framework, whose activated state possesses the coexistence of Lewis acid–base sites including 4-coordinated Zn²⁺ ions, 7-coordinated Ba²⁺ ions, uncoordinated carboxyl oxygen atoms, and N_pyridine atoms. Catalytic experiments exhibited that activated NUC-51a possesses a high catalytic activity on the cycloaddition reactions of epoxides with CO₂ at 55 °C, which can be ascribed to its structural advantages of nanoscale channels and rich bifunctional active sites. Moreover, NUC-51a could significantly accelerate the deacetalization-Knoevenagel condensation reaction in DMSO solvent at 70 °C.