Insights into Supported Copper(II)-Catalyzed Azide-Alkyne Cycloaddition in Water

Cross-linked polymeric ionic liquid material-supported copper (Cu-CPSIL), imidazolium-loaded Merrifield resin-supported copper (Cu-PSIL) and silica dispersed CuO (CuO/SiO(2)), were prepared and proved to be efficient catalysts for the one-pot synthesis of 1,4-disubsituted-1,2,3-triazoles by the reaction of alkyl halides with sodium azide and terminal alkynes in water at room temperature. Moreover, these supported copper catalysts were recovered quantitatively from the reaction mixture by simple filtration and reused for five consecutive recycles without significant loss of catalytic activity. Among the three immobilized copper catalysts, Cu-CPSIL exhibited excellent catalytic activity for the reaction of aliphatic bromides, sodium azide and terminal alkynes. The differences in the catalytic performances of the catalysts could be ascribed to the copper dispersion and the interaction between copper and the supports. In addition, water was used as the reaction media and the proton provider, the latter was found to be very important for the reaction. The XPS results suggested that the supported Cu(II) catalysts were reduced to catalytic Cu(I) species via alkynes homocoupling reaction. By means of IR and ESI-MS studies, a possible mechanism of cycloaddition based on the reduction of Cu(II) to Cu(I) species was proposed.