Development of a New Generation of Gold Catalysts for Amine Oxidation

A new type of outstandingly active gold catalysts has been developed for the aerobic oxidation of amines to imines. The gold nanoparticles are generated in situ in an organic medium prior to the oxidation reaction. Various gold salts, preferably AuCl3 and HAuCl4 center dot 3H(2)O, can be applied in the presence of nanoceria and the amine substrate acts as the reducing agent. The synergism between gold and ceria evacuated at 200 degrees C has a remarkable positive effect on the oxidation activity. The catalysts have been tested in the oxidation of dibenzylamine, N-tert-butylbenzylamine, and indoline. Apparently, the presence of organic and inorganic residue after the in situ catalyst preparation does not diminish the oxidation activity of gold. An alternative, less efficient route is the quantitative adsorption of [Au(PPh3)Cl] precursor onto ceria in an organic medium; and the subsequent ex situ evolution of gold nanoparticles (ca. 5 nm) via calcination at 250-400 degrees C. This catalyst is still ten-fold more active than conventional supported gold nanoparticles. In addition, it is free from impurities evolving during the in situ preparation and thus may find application in reactions other than amine oxidation.