Palladium-free and ligand-free Sonogashira cross-coupling
Copper nanoclusters catalyse the cross-coupling of alkynes and aryl halides to give the corresponding disubstituted alkynes. No palladium, ligand, or co-catalyst is needed, and products are isolated in good yields (80–85%) and high selectivity. The clusters are simple to prepare, stable and can be applied to a variety of iodo- and bromoaryls. Mechanistic pathways for homocoupling and cross-coupling of alkynes are examined by comparing the activity of different catalyst and co-catalyst combinations. The copper clusters show different catalytic properties than their homogeneous analogues.