Reaction of arylhydroxylamines with [Pd(Neoc)(NO3)2] (Neoc = neocuproine) : Non-innocent behavior of the nitrate anion

In an effort to understand the first stages of the reduction of nitroarenes to anilines by palladium/phenanthroline complexes and suspecting that arylhydroxylaminato complexes may be intermediates in this process, we investigated the reactivity of [Pd(Neoc)(NO3)(2)] (Neoc = neocuproine = 2,9-dimethyl-1,10-phenanthroline) with 3,5-dichlorophenylhydroxylamine. Spectroscopic evidence indicates that the desired [Pd(Neoc)(ONHC6H3Cl2)(NO3)] is indeed formed, but the complex is not stable and decomposes within a few hours. Two of the decomposition products were characterized by single crystal X-ray diffraction. They are a N-aryl-N-nitrosohydroxylaminato complex, [Pd(Neoc)(ON(3,5-C6H3Cl2) NO)][NO3] (major decomposition product) and a nitro-nitrate complex [Pd(Neoc)(NO2)(NO3)]. The results indicate that the nitrate ion is not innocent in the starting complex and oxidize hydroxylamine, being reduced itself to NO2 and NO.