Relative Bond Dissociation Energies for Two-Ligand Complexes of Cu+ with Organic Molecules in the Gas Phase

Article abstract of DOI:10.1021/ja00372a030

Ralative two-ligand dissociation enthalpies, δD(Cu⁺-2L), for Cu⁺ with 43 organic molecules are determined.A pulsed-laser volatilization/ionization sourse is used to generate Cu⁺ which reacts with EtCl and/or other molecules to give Cu(ligand)2⁺ species.Equilibrium constants are measured for the ligand-exchange reactions which occur when pairs of ligand molecules are present.Free energies for two-ligand exchange are obtained from the equilibrium constant for the reaction Cu(A)2⁺ + 2B ->/<- Cu(B)2⁺ + 2A.The free-energiy differences are added to give a scale of relative free energies for ligand exchange.These are converted to enthalpies to give δD(Cu⁺-2L) scale with the assumption that enthropy changes are small and can be neglected except for symmetry corrections which are made in appropriate cases.Dependence of δD(Cu⁺-2L) on functional group and substituent effects is analyzed.These results for Cu⁺ are compared to available results for other reference acids: H⁺, Al⁺, Mn⁺, Li⁺, and CpNi⁺.These comparisons show that Cu⁺ is a softer acid than the other reference acids.This is apparent from the relative preference of Cu⁺ for mercaptans and HCN compared to alcohols and other oxygen bases.