Bonding Energetics of Palladium-amido/aryloxide Complexes in DMSO: Implications for Pd-mediated Aniline Activation.

Thermodynamic knowledge of the metal-ligand (M-L) σ-bond strength is crucial to understanding metal-mediated transformations, but it is rarely presented in literature. Here, we developed a general methodology for determining the Pd-X (X = OR and NHAr) bond heterolysis energies (ΔGhet(Pd-X)) in DMSO taking [(tmeda)PdArX] (tmeda = N,N,N',N'-tetramethylethylenediamine) as the model complexes. The first ΔGhet(Pd-X) scales here derived span a range of 2.6-9.0 kcal/mol for ΔGhet(Pd-O)s and of 14.5-19.5 kcal/mol for ΔGhet(Pd-N)s, respectively, implying a facile heterolytic detachment of the Pd-ligands. Structure-reactivity analyses of a modeling Pd-mediated X-H bond activation reveal that the M-X bond metathesis is basically dominated by the differences of the X-H and Pd-X bond strengths, with the former being more influential. Combinatorial application of the ΔGhet(Pd-X) and pKa(X-H) parameters enables rational regulations of the reaction thermodynamics and chemo-selectivity, and hence provides a feasible energetic criterion for diagnosing the probability of aniline activation with Pd-X complexes.