A supramolecular recyclable catalyst for aqueous Suzuki-Miyaura coupling

A water-soluble, supramolecular catalytic system has been designed based on inclusion complexation between a hydrophobic palladium(II)-dipyrazole complex bearing an adamantyl (Ad) molecular recognition moiety and a complementary, hydrophilic beta-cyclodextrin (beta-CD) derivative. The single-crystal molecular structure of the Pd(II) complex was determined and its host-guest inclusion complexation with heptakis(2,6-di-O-methyl)-beta-CD (dm beta-CD) in an aqueous medium was confirmed by 2D NOESY H-1 NMR spectroscopy. The catalyst showed high activity for Suzuki-Miyaura coupling of hydrophilic aryl bromides with aryl boronic acids in aqueous organic solvents. In the presence of n-Bu4NBr as a stabilizer, the catalyst-containing reaction solution can be recycled and reused multiple times to catalyze the coupling reaction of fresh substrates once the product has been removed by centrifugation. This work demonstrates a supramolecular complex approach, non-covalently modifying a water insoluble metal complex to provide a water-soluble inclusion system to serve as a recyclable catalyst for potential application in green chemical synthesis.