A Precise Preparation Strategy for 2D Nanoporous Thulium-Organic Framework: High Catalytic Performance in CO2-Epoxide Cycloaddition and Knoevenagel Condensation

Abstract

Efficient conversion of carbon dioxide (CO₂) into high-value chemicals is viewed as one of the most promising approaches for solving the problem of an energy shortage and serious environment pollution. However, design and synthesis of confined multifunctional catalysts with in situ engineered task-specific sites and nanoporous environments remain a complex and challenging task due to a lack of in-depth understanding of their structure and reaction mechanism. Herein, we report a highly robust 2D nanoporous framework of {[Tm(HFPDC)(DMF)₂]·DMF·H₂O}_n (NUC-120) (H₄FPDC = 4,4′-(4-(4-fluorophenyl)pyridine-2,6-diyl)diisophthalic acid). The thermally activated host framework of [Tm(HFPDC)]_n (NUC-120a) has the following two merits: (i) nanoporous structure, (ii) massive quantity of functional sites. Moreover, NUC-120 and activated NUC-120a display high thermal and chemical stability, which have been proved by TGA and the soaking experiments in acid–base water and most organic solvents. Catalytic experiments proved that NUC-120a, in the presence of the n-Bu₄NBr cocatalyst could efficiently catalyze the coupling reaction of CO₂ and epoxides under comparatively mild conditions. Furthermore, NUC-120a also displays high catalytic performance in the Knoevenagel condensation reactions of aldehydes and malononitrile, which should be because the coexisting Lewis acidic and basic sites can separately activate aldehyde and malononitrile molecules. Thereby, this work further provides insight that desired functional materials can be generated by using the existing suitable secondary building units (SBUs) and meticulously regulating the growth environments.