Synthesis and characterization of Cu@Hal, an effective heterogeneous catalyst for aqueous multicomponent azide‐alkyne [3+2] cycloaddition reactions

The synthesis of a nanocomposite material consisting of Cu nanoparticles encapsulated in halloysite nanotubes (Cu@Hal) was achieved by the reduction of Cu(NO 3 ) 2 ⋅ 3H 2 O with sodium ascorbate/sodium borohydride in an aqueous suspension of trisodium citrate and halloysite. The nanocomposite was found to be an effective heterogeneous catalyst for the multicomponent copper catalyzed azide‐alkyne cycloaddition reaction (CuAAC). A variety of terminal alkynes reacted with benzyl halides and sodium azide in the presence of Cu@Hal in water. In situ formation of the organic azides afforded the corresponding 1,4‐disubstituted 1,2,3‐triazoles regioselectivily, in excellent yields. The catalyst was easily recovered and recycled without loss of activity with low metal leaching.