Nanoporous {Y2}‑Organic Frameworks for Excellent Catalytic Performance on the Cycloaddition Reaction of Epoxides with CO2 and Deacetalization–Knoevenagel Condensation

Stable metal–organic frameworks containing periodically arranged nanosized pores and active Lewis acid–base active sites are considered as ideal candidates for efficient heterogeneous catalysis. Herein, the exquisite combination of [Y2(CO2)7(H2O)2] cluster (abbreviated as {Y2}) and multifunctional linker of 2,4,6-tri­(2,4-dicarboxyphenyl)­pyridine (H6TDP) led to a nanoporous framework of {[Y2(TDP)­(H2O)2]·5H2O·4DMF}n (NUC-53, NUC = North University of China), which is a rarely reported binuclear three-dimensional (3D) framework with hierarchical tetragonal-microporous (0.78 nm) and octagonal-nanoporous (1.75 nm) channels. The inner walls of these channels are aligned by {Y2} clusters and plentifully coexisted Lewis acid–base sites of YIII ions and Npyridine atoms. Furthermore, NUC-53 has a quite large void volume of ∼65.2%, which is significantly higher than most documented 3D rare-earth-based MOFs. The performed catalytic experiments exhibited that activated NUC-53 showed a high catalytic activity on the cycloaddition reactions of CO2 with styrene oxide under mild conditions with excellent turnover number (TON: 1980) and turnover frequency (TOF: 495 h–1). Moreover, the deacetalization–Knoevenagel condensation reactions of benzaldehyde dimethyl acetal and malononitrile could be efficiently prompted by the heterogeneous catalyst of NUC-53. These findings not only pave the way for the construction of nanoporous MOF based on rare-earth clusters with a variety of catalytic activities but also provide some new insights into the catalytic mechanism.具有周期性排布纳米级孔道与活性路易斯酸碱位点（Lewis acid–base sites）的稳定金属有机框架（metal–organic frameworks, MOFs）被视为高效多相催化的理想候选材料。本文中，[Y₂(CO₂)₇(H₂O)₂]簇（缩写为{Y₂}）与多功能配体2,4,6-三(2,4-二羧基苯基)吡啶（H₆TDP）经巧妙组装，得到纳米孔框架化合物{[Y₂(TDP)(H₂O)₂]·5H₂O·4DMF}ₙ（命名为NUC-53，其中NUC为中北大学（North University of China）的缩写）。该化合物是一种鲜有报道的双核三维（3D）骨架，拥有分级排布的四方微孔（0.78 nm）与八边形纳米孔（1.75 nm）通道；其通道内壁由{Y₂}簇修饰，同时共存着大量由三价钇离子与吡啶氮原子构成的路易斯酸碱活性位点。此外，NUC-53的空隙体积占比约为65.2%，显著高于多数已报道的三维稀土基MOFs。所开展的催化实验结果显示，活化后的NUC-53在温和条件下对二氧化碳与环氧苯乙烯的环加成反应表现出优异的催化活性，其转化数（turnover number, TON）达1980，转化频率（turnover frequency, TOF）为495 h⁻¹；同时该多相催化剂还可高效催化苯甲醛二甲缩醛与丙二腈的脱缩醛-Knoevenagel缩合反应。本研究不仅为基于稀土簇构建具有多样催化活性的纳米孔MOFs开辟了新途径，也为相关催化机制的研究提供了全新视角。