Synthesis and Properties of “Sandwich” Diimine-Coinage Metal Ethylene Complexes

Synthesis and full characterization of cationic isostructural “sandwich” diimine-coinage metal ethylene complexes are reported. Ethylene self-exchange kinetics proceeds by an associative exchange mechanism for Cu and Au complexes. The fastest ligand exchange was observed for Ag complex 8a. The upper limit of ΔG⧧, assuming associative ligand exchange, was found to be ca. 5.0 kcal/mol. Ethylene self-exchange in Cu complex 7b proceeds with ΔG298⧧ = 12.9 ± 0.1 kcal/mol, while the exchange is the slowest in Au complex 9, with ΔG298⧧ = 16.7 ± 0.1 kcal/mol. Copper complex 7b is unusually stable and can survive in air for years.