Are homoleptic complexes of ethylene with group 12 metals isolable in solution? A DFT study

Ethylene efficiently binds late transition metals of groups 10 and 11. In spite of their reactivity, homoleptic compounds of formula [M-(η²-C₂H₄)₃]ⁿ⁺ (with n = 0,1) have been isolated in solution and solid state and characterized spectroscopically throughout the last 50 years with metals from groups 10 and 11. X-ray diffraction studies proved that such homoleptic adducts adopt planar “wheel” structures where ethylene moieties lies flat in the same plane both in group 10 and 11. These experimental findings were also confirmed by several in-depth computational investigations carried out to understand the bond pattern of such peculiar structures. Homoleptic complexes of group 10 and 11 metals with ethylene are normally obtained in poorly coordinating solvents (like CH₂Cl₂ or light petroleum) saturated with ethylene to increase the stability of such species in solution. In the case of coinage metals, Cu(I), Ag(I) and Au(I), weakly coordinating fluorinated counter-ions (like SbF₆⁻) succeeded in stabilize the ethylene adducts, but, curiously, no analogous success has been reported for Zn(II), Cd(II), and Hg(II). Isoelectronic congeners along group 12 are still elusive, however, and, to our knowledge, full experimental and theoretical characterizations are still missing. This manuscript focuses on the theoretical study of the thermodynamic stability and properties of homoleptic complexes of ethylene with metals from group 12 in comparison with those from groups 10 and 11.