Catalysis Letters, Vol.143, No.6, 572-577, 2013
[Cu-8(mu(4)-H){S2P(OEt)(2)}(6)](PF6): A Novel Catalytic Hydride-Centered Copper Cluster for Azide-Alkyne Cycloaddtion
A hydride-centered dithiophosphate cluster [Cu-8(mu(4)-H){S2P(OEt)(2)}(6)](PF6) (1)] previously developed by us was applied as a new catalyst to the 1,3-dipolar cycloaddition of organic azides and alkynes for preparing substituted trizoles. With the required catalyst loading as low as 0.4 mol%, the reactions of terminal alkynes with BnN3 all proceeded smoothly at ambient temperature in CH3CN to exclusively produce 1,4-triazoles in good yields. For these reactions, it is assumed that the formation of the requisite copper acetylide intermediate is facilitated by the abstraction of the terminal hydrogen of alkynes by the hydride released from the central of the cluster. With only few examples being documented in literatures, the reactions of a range of internal alkynes have also been realized under the catalysis of 1 (0.8 mol%) in DMF at elevated temperature, to yield 1,4,5-trisubstituted triazoles in moderate to high yields. Our study has provided a preliminary insight into the effect of sulfur-based ligands on the activity of copper ion.