Zirconium-Catalyzed Amine Oxidation: A Mechanistic Study

The zirconium-catalyzed oxidation of amines in the presence of hydroperoxides gives the corresponding nitro compounds in high yields. In the present paper, we describe mechanistic details of this three-step oxidation, which was investigated by means of DFT calculations. It is shown that N-oxides, hydroxylamines, and nitroso derivatives are formed as intermediates. These compounds had already been postulated on the basis of synthetic experiments. During the oxidation process, the nitrogen atom changes its electronic character from a strong nucleophilic center to a moderate electrophilic center; this is reflected by the geometry of the transition states of the oxygen-transfer process.