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.
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