Mechanism of Enolate Transfer between Si and Cu

Exchange of X (F, Cl, OMe) and a substituted enolate chain between SiMe₃ and various Cu^I complexes was examined. Reaction mechanisms pass through a cyclic transition state in which the reaction coordinate is associated with rotation of the SiMe₃ moiety. The dependence of the thermodynamic and kinetic features on the nature of the active and ancillary ligands was examined. Formation of copper enolate is shown to be favored when stabilized enolates are used. Replacement of F by Cl reverses the preference of the reaction. This is associated with the small difference between the Cu-Cl and Si-Cl bond energies, in contrast to other Si-X bonds, which are systematically stronger than their Cu-X analogues.