An Abnormal N-Heterocyclic Carbene-Copper(I) Complex in Click Chemistry

Herein we report the synthesis of a copper(I) chloro complex using an abnormal N-heterocyclic carbene (aNHC) salt, 1,3-bis(2,6-diisopropylphenyl)-2,4-diphenylimidazolium. The CuCl(aNHC) complex efficiently catalyzed Huisgen 1,3-dipolar cycloaddition reactions (click reactions) of azides with alkynes to give 1,4-substituted 1,2,3-triazoles in excellent yields at room temperature within short reaction time under solvent-free conditions. The catalyst successfully activated benzyl azide and phenylacetylene under the low catalyst loading of 0.005mol% resulting in a nearly quantitative yield of the product at room temperature with the high TON value of 19,800. The catalyst also exhibits high efficiency in the reaction between sterically hindered azides and alkynes under solvent-free conditions at room temperature. Furthermore, a number of internal alkynes was successfully tested in this copper-catalyzed cycloaddition reaction for synthesis of 4,5-disubstituted triazoles.