Scheme 5. Revised mechanism for the formation of product 2a (CuL = CuMeCN). Relative free energies (ΔG, in kcal mol⁻¹) of the key intermediates and transition states are calculated at the SMD(toluene)-M06/6-31G(d,p)/LANL2DZ level of theory at 298 K. Key bond lengths are shown in bold (unit: Å).