Theoretical Studies of the Mechanism of Aerobic Alcohol Oxidation with Palladium Catalyst Systems

Density functional theory (DFT) was applied to a comprehensive mechanistic study of the
Pd(II)-catalyzed oxidation of alcohols by molecular oxygen. Both parts of the catalytic cycle,
i.e., the oxidative dehydrogenation of the substrate and the regeneration of the catalyst by
the co-oxidant, molecular oxygen, were studied. The catalytic cycle under consideration
consists of intramolecular deprotonation, β-hydride elimination, and migratory insertion
steps, and it is relevant for a wide class of catalytic systems. In particular, a Pd(II)
cyclometalated system was addressed and qualitatively compared with the Uemura system
(Pd(OAc)2/pyridine) and with the Pd−carbene system. Geometries of the intermediate
complexes and relative Gibbs free energies were identified along the proposed reaction path
with the help of computational methods. The transition state for the β-hydride elimination,
which is the highest point on the energy profile of the catalytic cycle, was identified.