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

Herein, the rare combination of BaII (5s) and ZnII (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 [BaIIZnII(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 Npyridine 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.