Abstract
Herein, we report a Pd4L2-type molecular cage (1) and catalyzed reactions of spiroepoxy naphthalenone (2) in water, where selective formation of 2-(hydroxymethyl)naphthalene-1,4-dione (3) via aerobic oxidation, or 1-hydroxy-2-naphthaldehyde (4) via photo-induced rearrangement under N2 have been accomplished. Encapsulation of four molecules of guest 2 within cage 1, i.e., (2)4⊂1, has been confirmed by NMR, and a final host-guest complex of 3⊂1 has also been determined by single crystal X-Ray diffraction study. While the photo-induced ring-opening isomerization from 2 to 4 are known, appearance of charge-transfer absorption on the host-guest complex of (2)4⊂1 allows low-power blue LEDs irradiation to promote this process.
Highlights
Artificial supramolecular architectures constructed via self-assembly with metal ions and organic ligands have attached tremendous attentions due to aesthetic structural diversity [1,2,3,4,5,6,7,8,9,10,11,12] and bio-mimic catalysis [13,14]
For the cage promoted reactions, it is generally accepted that enhanced effective concentration and the pre-organization effect imposed to the guest molecules by the cage cavity contribute to the accelerated reaction rate and the improved product selectivity
The crystals were of sufficient quality and X-ray crystallography established the structure of the new host–guest complex, which contained product 3 and cage 1 (Appendix A)
Summary
Artificial supramolecular architectures constructed via self-assembly with metal ions and organic ligands have attached tremendous attentions due to aesthetic structural diversity [1,2,3,4,5,6,7,8,9,10,11,12] and bio-mimic catalysis [13,14]. Coordination molecular cages have been extensively studied as artificial enzyme-mimics to promote various reactions of the contained molecules within the confined space [15,16,17,18,19]. We report that cage 1 promoted aerobic oxidation and photo-induced isomerization reactions in water from spiroepoxy naphthalenone 2. In the presence of cage 1, both naphthoquinone 3 and Catalysts 2021, 11, 484 reactions in water from spiroepoxy naphthalenone 2. Considering that conversion from 2 to 3 is a competition pathway under air in the presence of cage 1, this photo-induced isomerization has to be carried out under N2 atmosphere.
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