Gold(III) complexes catalyze deoximations/transoximations at neutral pH.

The reaction of gold trihalides with reducing agents such as thiols, sodium borohydride, and hydroxylamine results in gold nanoparticles (AuNPs). In particular, NH2OH is used to facilitate the growth of smaller particles or the formation of thin films of gold. Our interest in developing a mild catalytic method for the conversion of nitro, oxime, and nitrone groups into carbonyl groups led us to examine the interaction of gold(III) with simple oximes as a potential approach for deoximation. The hydrolysis of the coordination complexes of oximes and glyoximes with gold(III) has not been investigated. If a partial hydrolysis of oximes into RR’C=O and NH2OH took place, NH2OH would be oxidized in situ by gold(III), and the equilibrium would be shifted 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 when possible at room temperature. A polyfunctional molecule containing groups that are prone to hydrolysis should survive under these reaction conditions. Lewis acids that are soluble and stable in aqueous media, that is Sc(OTf)3, LaCl3·7H2O, FeXn, RuCl3, RhCl3, PtCl4, CuX2, AuX3, InBr3, and related compounds were screened as catalysts for the hydrolysis of 4-phenyl-2butanone oxime (Table 1). Only AuBr3 (99.9%) and AuCl3 (99.99%) promoted the hydrolysis of 4-phenyl-2-butanone oxime when the pH was adjusted to pH 7 with a standard solution of NaOH (1.000m, 99.99%; entries 19–27). Except for AuX3, none of these salts was a suitable initiator or catalyst at pH 4–8; in fact, in most cases when the solutions were neutralized, the corresponding hydroxides or oxide hydrates precipitated out of solution, as expected. Despite their lack of solubility in water, we also examined a platinum(II) salt (entry 8), copper(I) salts (entries 10–14), and a gold(I) salt (entry 17), because of their success as catalysts in other contexts, but no effect was observed. Among all these common transition-metal cations, only the gold(III)