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)(3)Cu][SbF6] has been synthesized using cyclooctyne and in situ generated CuSbF6. Tris(alkyne) silver complexes [(cyclooctyne)(3)Ag](+) involving weakly coordinating counterions such as [SbF6](-) and [PF6](-) have also been isolated in good yield using cyclooctyne and commercially available AgSbF6 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)(3)Cu][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)(2)Cl and AgSbF6 in dichloromethane. The gold atom of [(cyclooctyne)(2)Au](+) 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)(3)M](+), [(cyclooctyne)(2)M](+), and [(cyclooctyne)M](+) and neutral [(cyclooctyne)(2)MCl] 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.