The synthesis of (η2/25-2-butyne)copper(I) hexafluoroacetylacetonate was achieved in one step and in good yield. X-ray crystallographic examination revealed two structurally similar, nearly planar molecules within the monoclinic crystal. The 2-butyne ligand is η2bonded, parallel to the Cu /S-diketonate plane, the methyl groups are cis bent away from copper (θCCMo= 163°) with a small angle of deformation from linear and the C≡C bond distance averages 1.210 Å. All of the data indicate π-electron donation from the butyne ligand to the copper(I) center and minimal π-back-bonding to the alkyne. This previously unreported complex is a volatile yellow solid which undergoes pyrolytic decomposition to copper metal. Chemical vapor deposition of high-purity copper films with rapid rates of deposition and good conformality were observed upon pyrolytic decomposition from this complex. © 1992, American Chemical Society. All rights reserved.