(Alkyne)(2,2′-bipyridine)copper(I) complexes. Controlled formation of [Cu(bpy)(alkyne)]+ and {[Cu(bpy)]2(alkyne)}2+

Article abstract of DOI:10.1021/om00037a019

The addition of 1 equiv of 2,2′-bipyridine (bpy) to a solution of Cu(NCMe)₄X (X = PF₆^--, SbF₆^-) followed by addition of an excess of alkyne (alkyne = 3-hexyne, 1-pentyne, methyl 2-butynoate, diphenylacetylene, diethyl acetylenedicarboxylate, phenylacetylene) leads to the preparation of [Cu(bpy)(alkyne)]X complexes in good yield. In order to isolate pure products, the alkyne complexes must be precipitated in the presence of excess alkyne. The alkyne ligands are labile in solution, exchanging rapidly on the NMR time scale. Competition studies show that the relative affinities of the alkynes (and ethylene) for copper in this system are C₂H₄ ～ HC≡CPr > EtC≡CEt ～ DEAD > HC≡CPh > MeC≡CCO₂Me > PhC≡CPh. Repeated precipitation from solutions that initially contain [Cu(bpy)(alkyne)]X (alkyne = diethyl acetylenedicarboxylate, phenylacetylene) complexes in the absence of added alkyne leads to the isolation of {[Cu-(bpy)]₂(alkyne)}X₂, complexes with a 2:1 copper:alkyne stoichiometry.