Butterfly-Like Tetranuclear Copper(I) Clusters For Efficient Alkyne Homocoupling Reactions

In this work, we here prepare a new tetranuclear Cu-I cluster with a precise configuration of Cu-4(PPh3)(4)(bis(prop-2-ynyloxy)biphenyl)(2). X-ray single-crystal diffraction shows that the bi-alkynyl ligands bind to two Cu atoms via a sigma-bond and to the other two Cu atoms via a pi-bond configuration, presenting a new alkynyl-Cu motif and a butterfly-like framework. Cu-4(PPh3)(4)L-2 clusters exhibit photoluminescence property at 410 and 505 nm. Cu-4(PPh3)(4)L-2 clusters also give good performances in the alkyne homocoupling reactions after its immobilization on different oxides. The copper(I) species is proved to be the catalytic active site during the homocoupling reactions. And the basic property of the oxides (e. g. NiO) can promote the coupling catalysis, and a side-group effect of the alkyne reactants is distinctly observed. In all, this study extends the catalytic application of the copper clusters to the carbon-carbon coupling reactions and gives some cue to develop the potential exploitation of copper clusters in other organic transformations.