Binding Interactions in Copper, Silver and Gold pi-Complexes

The copper(I), silver(I), and gold(I) metals bind π-ligands by σ-bonding and π-back bonding interactions. These interactions were investigated using bidentate ancillary ligands with electron donating and withdrawing substituents. The π-ligands span from ethylene to larger terminal and internal alkenes and alkynes. Results of X-ray crystallography, NMR, and IR spectroscopy and gas phase experiments show that the binding energies increase in the order AgCuAu and the binding energies are slightly higher for alkynes than for alkenes. Modulation of the electron density at the metal using substituents on the ancillary ligands shows that the π-back bonding interaction plays a dominant role for the binding in the copper and gold complexes.