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

Abstract

The tris(alkyne) copper complex [(cyclooctyne)3Cu][SbF6] 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 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)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.