Tris(alkyne) and bis(alkyne) complexes of coinage metals: Synthesis and characterization of (cyclooctyne)₃M⁺ (M = Cu, Ag) and (cyclooctyne)₂Au⁺ and coinage metal (M = Cu, Ag, Au) family group trends

The tris(alkyne) copper complex [(cyclooctyne)₃Cu][SbF ₆] has been synthesized using cyclooctyne and in situ generated CuSbF₆. Tris(alkyne) silver complexes [(cyclooctyne) ₃Ag]⁺ involving weakly coordinating counterions such as [SbF₆]^- and [PF₆]^- have also been isolated in good yield using cyclooctyne and commercially available AgSbF ₆ and AgPF₆. These coinage metal tris(alkyne) adducts have trigonal-planar metal sites. The alkyne carbon atoms and the metal site form distorted spoke-wheel (rather than upright trigonal-prismatic) structures in the solid state. In [(cyclooctyne)₃Cu][SbF₆], these distortions result in a propeller-like arrangement of alkynes. A cationic gold(I) complex having two alkynes has been prepared by a reaction of equimolar amounts of Au(cyclooctyne)₂Cl and AgSbF₆ in dichloromethane. The gold atom of [(cyclooctyne)₂Au]⁺ coordinates to the cyclooctynes in a linear fashion, while the carbon atoms of the alkyne groups form a tetrahedron around gold(I). Optimized geometries of cationic [(cyclooctyne)₃M]⁺, [(cyclooctyne) ₂M]⁺, and [(cyclooctyne)M]⁺ and neutral [(cyclooctyne)₂MCl] and [(cyclooctyne)MCl] adducts (M = Cu, Ag, Au) using density functional theory (DFT) at the BP86/def2-TZVPP level of theory and a detailed analysis of metal-alkyne bonding interactions are also presented.