Supramolecular synthesis of coumarin derivatives catalyzed by a coordination-assembled cage in aqueous solution
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A self-assembled Pd4L2 cage is employed as a water-soluble molecular flask for the synthesis of functionalized coumarins from a series of salicylaldehyde derivatives and cyanoacetates/malononitrile. The catalytic reaction features mild aqueous conditions and broad substrate scope. Crystal structures of the host-guest complexes for two substrates and one analogous intermediate have been obtained, shedding light on the supramolecular reaction mechanism. Michaelis-Menten kinetic studies were performed in one typical case, revealing that the rate of product formation has been enhanced by over 23-fold in contrast to the background reaction without cage. Moreover, the same reaction catalyzed by a smaller Pd6L4 cage gives a mixture of products and much lower yields, suggesting that fine-tuning on the size and symmetry of the cages’ cavity is crucial for their applications in supramolecular catalysis.
Keywordscoordination-assembly cage encapsulation Knoevenagel condensation
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This work was supported by the National Natural Science Foundation of China (21825107, 21601183, 21801241, 21571090), Natural Science Foundation of Fujian Province (2016J05051, 2017J05037), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB20000000). We thank the staff of BL17B beamline at National Centre for Protein Sciences Shanghai and Shanghai Synchrotron Radiation Facility, Shanghai, China, for assistance during X-ray data collection.