Selectivity Switch in the Aerobic 1,2-Propandiol Oxidation Catalyzed by Diamine-Stabilized Palladium Nanoparticles

Palladium nanoparticles stabilized by a sterically demanding secondary diamine ligand have been synthesized by hydrogen reduction of a palladium acetate complex bearing the corresponding diimine ligand. The obtained nanoparticles were used to catalyze the aerobic oxidation of 1,2-propandiol in n -hexane, and after their heterogenization onto a high surface area carbon, in water. In n -hexane 2,4-dimethyl-1,3-dioxolan-2-yl ( i.e ketal formed between hydroxyacetone and 1,2-propandiol) has been obtained as major product with a selectivity of > 80%, whereas in water acetic acid with a selectivity of > 85% has been achieved. The selectivity switch observed was a clear induced by water. The robustness of diamine-stabilized palladium nanoparticles under real aerobic oxidation conditions has been proved by recycling experiments, TEM measurements of the recovered catalysts and by comparison of its performance with that of palladium nanoparticles generated by the metal vapor synthesis technique and supported onto the same carbon in the absence of the stabilizing diamine ligand.