Au Complexes Catalyze Deoximations/Transoximations at Neutral pH**

Reaction of gold trihalides with reducing agents such as thiols, NaBH4 or hydroxylamine gives gold nanoparticles (Au NPs). In particular, NH2OH is used to produce monodisperse colloidal Au NPs by “growing” of smaller particles or to form thin films of Au on glass substrates. Our interest in developing a mild catalytic method for the conversion of nitro/oxime/nitrone groups to carbonyl groups led us to examine first the interaction of gold(III) with simple oximes as a potential deoximation procedure. The hydrolysis of the coordination complexes of oximes and glyoximes with gold(III) has not been investigated. If a partial hydrolysis of oximes (to RR’C=O and NH2OH) took place, NH2OH would be oxidized in situ by Au, shifting the equilibrium to the right. Our first challenge was to find a water-soluble and stable gold complex that could catalyze the hydrolysis of the robust oxime group at neutral pH and, as far as possible, at room temperature (RT). Under these conditions, prone-to-hydrolysis characteristic and protecting groups contained in a polyfunctional molecule would be compatible (or would have the highest chances of survival). To our delight, only AuBr3 (99.9%) and AuCl3 (99.99%) were capable, adjusting the pH with a standard solution of NaOH 1.000 M (99.99%), of promoting the hydrolysis of 4-phenyl-2-butanone oxime (Table 1), after screening Lewis acids that are quite soluble and stable in aqueous media [Sc(OTf)3, LaCl3·7H2O, FeXn, RuCl3, RhCl3, PtCl4, CuX2, AuX3, InBr3] and related compounds. Save AuX3, none of these salts was a suitable initiator or catalyst at pH 4–8; in fact, when the solutions of most of them were neutralized, the corresponding hydroxydes or oxide hydrates precipitated, as expected. Despite their lack of solubility in water, we also examined Pt, see entry 8, Cu, see entries 10–12, and Au salts, entry 17, because of their excellence as catalysts in other contexts, but no effect was observed. In short, among all these common transition metal cations, only Au species did work at neutral pH. However, 50 mol % of Au was required to complete the hydrolysis of 4-phenyl-2-butanone oxime (entry 21), as the active Au species disappeared by reduction to Au NPs by NH2OH (as expected). Thus, the next challenge was to develop a truly catalytic version of this hydrolysis (a cheaper process). We explored the possibility of trapping NH2OH with carbonyl compounds capable of forming oximes more stable than the starting oxime (Table 1, entries 22–27). The best results for such a transoximation process were obtained with methyl _______________________________________________________