Use of [SbF₆]⁻ to Isolate Cationic Copper and Silver Adducts with More than One Ethylene on the Metal Center

A cationic tris­(ethylene)­copper­(I) and tris­(ethylene)­silver­(I) adduct has been isolated using hexafluoroantimonate counterion. X-ray crystallographic analysis shows that the metal atom in these adducts coordinates to three ethylene molecules in a trigonal planar fashion, forming a spoke-wheel arrangement. In [M­(C2H4)3]­[SbF6] adducts (M = Cu, Ag, Au), the average M–C distances of 2.189 Å for Cu and 2.410 Å for Ag can be compared with the corresponding distance of 2.268 Å for Au and show that the copper­(I) complex has the shortest while the silver adduct displays the longest M–C distances. These agree well with the computed values (2.172, 2.408, and 2.308 Å for Cu, Ag, and Au analogues, respectively) and follow the same trend as the covalent radii of M­(I). Structural data on [μ3-Cl­{Cu­(C2H4)2}3]­[SbF6]2, which features bis­(ethylene)­copper­(I) moieties, are also presented. It has a trigonal planar Cu3Cl core with a triply bridging chloride ion bonded to three trigonal planar copper centers. Ethylene molecules are bonded in an η2-fashion. The data indicate that while these [M­(C2H4)3]+ complexes may be primarily electrostatic in their metal–ethylene binding, there remains an important covalent contribution, particularly for the copper and gold congeners.