Computational Insights into the Effect of Ligand Redox Properties on Reductive Elimination from Au(III), Pd(II), and Pt(II) Complexes

We computationally investigated the Ar–Ar reductive
elimination
process in a series of biaryl Au(III), Pd(II), and Pt(II) complexes
to explore the factors that govern the activation free energy associated
with C–C coupling (ΔG‡). Contrary to conventional beliefs that emphasize metal–Ar
bond strength as the primary determinant for the ease of reductive
elimination, our density functional theory (DFT) calculations reveal
that the key factor is the oxidation susceptibility of the Ar ligands
in their anionic forms: the easier the oxidation of Ar–, the lower the activation free energy (ΔG‡). Indeed, we found that ΔG‡ strongly correlates with the reduction potential
for the reaction Ar• + e– →
Ar– (E°(Ar)). We further demonstrate
that variations in complex net charge and metal center significantly
influence the electron-accepting ability of the metal center in the
transition state, thereby affecting the ease of reductive elimination.
Notably, the effects of these factors (net charge and metal center)
on the activation barrier were found to be largely independent of
the nature of the Ar ligands.