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Experimental evidence for the involvement of dinuclear alkynylcopper(I) complexes in alkyne-azide chemistry
Dinuclear alkynylcopper(I) ladderane complexes are prepared by a robust and simple protocol involving the reduction of Cu2(OH)3OAc or Cu(OAc)2 by easily oxidised alcohols in the presence of terminal alkynes; they function as efficient catalysts in copper-catalysed alkyne–azide cycloaddition reactions as predicted by the Ahlquist–Fokin calculations. The same copper(I) catalysts are formed during reactions by using the Sharpless–Fokin protocol. The experimental results also provide evidence that sodium ascorbate functions as a base to deprotonate terminal alkynes and additionally give a convincing alternative explanation for the fact that the CuI-catalysed reactions of certain 1,3-diazides with phenylacetylene give bis(triazoles) as the major products. The same dinuclear alkynylcopper(I) complexes also function as catalysts in cycloaddition reactions of azides with 1-iodoalkynes.
This work was supported by Loughborough University. BRB thanks Research Councils UK for a RCUK Fellowship.