Theoretical rationalisation for the mechanism of N-heterocyclic carbene-halide reductive elimination at Cu-III, Ag-III and Au-III

Reductive elimination of imidazolium salts from CuIII is extremely sensitive to the anionic ligand (X or Y) type on Cu (e.g. ΔG‡ ranges from 4.7 kcal mol-1 to 31.8 kcal mol-1, from chloride to benzyl). Weakly σ-donating ligands dramatically accelerate reductive elimination. Comparison with Ag/Au shows that the HOMO energy, strength of M-NHC and M-Y bonds and inherent stability of MIII with respect to MI are critical to governing reaction feasibility.