Acetoxime coordinates to palladium(II) and is catalytically hydrolysed to acetone

Several new palladium(II) complexes containing acetoxime as a unidentate li gand were synthesized from cis-[Pd(en)(solv)(2)](2+) 1a and cis-[Pd(dtod)(s olv)(2)](2+) 1b, in which the displaceable ligand solv is water or acetone, en is ethane-1,2-diamine, and dtod is 3,6-dithia-1,8-octanediol. The aceto xime complexes are characterized by UV-visible spectrophotometry and H-1 an d C-13 NMR spectroscopy in solution. Acetoxime in the mono-oxime complexes cis-[Pd(en){N(OH)C(CH3)(2)}(solv)](2+) 2a and cis-[Pd(dtod){N(OH)C(CH3)(2)} (solv)](2+) 2b undergoes hydrolysis to acetone and hydroxylamine. The propo sed mechanism involves internal attack of a Pd-II-bound hydroxo ligand at t he coordinated acetoxime. This palladium(II)-catalysed hydrolysis is at lea st 10(4) times faster than hydrolysis in the absence of a catalyst. The rat e enhancement arises from polarization of acetoxime upon coordination to pa lladium(II), the availability of the nucleophilic hydroxo ligand, and close proximity of these two species. The complex [Pd(dien){N(OH)C(CH3)(2)}](2+) , which contains the tridentate diethylenetriamine ligand, is almost unreac tive toward hydrolysis because it lacks a Pd-II-bound aqua or hydroxo ligan d, so that the reaction occurs via the less-favorable external attack of so lvent water. Acetoxime in the bis-acetoxime complex cis-[Pd(dtod){N(OH)C(CH 3)(2)}(2)](2+) 3b hydrolyses very slowly because this complex also lacks aq ua or hydroxo ligands. Therefore, this complex was crystallized and its str ucture determined by X-ray crystallography.