Highly Efficient Conversion of Aziridines and CO₂ Catalyzed by Microporous [Cu₁₂] Nanocages

The conversion of CO2 as a C1 source into value-added products is an attractive alternative in view of the green synthesis. Among the reported approaches, the cyclization reaction of aziridines with CO2 is of great significance since the generated N-containing cyclic skeletons are extensively found in pharmaceutical chemistry and industrial production. However, a low turnover number (TON) and homogeneous catalysts are often involved in this catalytic system. Herein, one novel copper–organic framework {[Cu2(L4–)(H2O)2]·3DMF·2H2O}n (1) (H4L = 2′-fluoro-[1,1′:4′,1″-Terphenyl]-3,3″,5,5″-tetracarboxylic acid) assembled by nanosized [Cu12] cages was successfully synthesized and structurally characterized, which exhibits high CO2/N2 selectivity due to the strong interactions between CO2 and open Cu(II) sites and ligands in the framework. Catalytic investigations suggest that 1 as a heterogeneous catalyst can effectively catalyze the cyclization of aziridines with CO2, and the TON can reach a record value of 90.5. Importantly, 1 displays excellent chemical stability, which can be recycled at least five times. The combination explorations of nuclear magnetic resonance (NMR), 13C-isotope labeling experiments, and density functional theory (DFT) clearly uncover the mechanism of this aziridine/CO2 coupling reaction system, in which 1 and tetrabutylammonium bromide (TBAB) can highly activate the substrate molecule, and the synergistic catalytic effect between them can greatly reduce the reaction energy barrier from 51.7 to 36.2 kcal/mol.