Ultrasonic exfoliation of a Cd-based metal–organic framework into ultrathin nanosheets for visible-light-initiated trifluoromethylation and sequential oxidation–cyclisation reactions

Abstract

We fabricated a two-dimensional (2D) Cd(II) metal–organic framework [Cd₂(ADPA)(H₂O)₂(NMP)₂]_n (denoted as XAIU-5; NMP = N-methylpyrrolidone) from Cd(NO₃)₂·4H₂O and 5,5′-(anthracene-9,10-diyl)diisophthalic acid (H₄ADPA). Single-crystal X-ray diffraction revealed that the layers are staggered, forming a 2D + 2D → three-dimensional (3D) supramolecular architecture. XAIU-5 vigorously photocatalysed the trifluoromethylation reaction and the sequential oxidation–cyclisation reaction under visible-light irradiation. Moreover, each Cd(II) center in the adjacent bimetallic motif is ligated by one water and one N-methyl-2-pyrrolidone molecule. Through density functional theory (DFT) calculation, it is found that water molecules are readily displaced during the reaction, thereby furnishing vacant active sites for the substrate molecules. Cd(II) acts as an electronic modulator that optimizes spin distribution, suppresses carrier recombination, and facilitates charge migration, thereby playing an essential role in the catalytic process. Ultrasonic exfoliation of XAIU-5 yielded single-layer structured nanosheets (XAIU-5-NS) with enhanced photocatalytic activity. This is attributed to the exposed straticulate Cd-ADPA units and reduced charge-transfer resistance, which facilitate electron–hole separation and substrate activation. The proposed strategy can sustainably synthesise trifluoromethyl drugs and thiazole, oxazole and imidazole products under visible light, indicating that catalyst nanosheets play a critical role in optimising photo-redox performance.