Reaction of K[PtCl 3 (Me 2 SO)] and 1,2-naphthoquinone-1-monoxime in water-dimethyl sulfoxide medium led to cis-(S,N)-[PtCl{2-(O)C 10 H 6 NO}(Me 2 SO)] 1. Chlorination of the latter in methanol readily generates, under mild conditions, the platinum() compound cis-(S,N)-[PtCl 3 {2-(O)C 10 H 5 Cl 2 (OMe)NO}(Me 2 SO)] 2 with a chelating nitrosonaphtholato ligand bearing a new chiral atom due to concomitant chlorination and nucleophilic addition of a MeOH solvent molecule. The newly formed ligand was liberated from 2 by reaction with excess thiourea. The chlorination course is strongly dependent on the nature of solvent employed and in CHCl 3 also at room temparature the chlorination with either Cl 2 or NOCl brings about only oxidation of the metal center to achieve cis-(S,N)-[PtCl 3 {2-(O)C 10 H 6 NO}(Me 2 SO)] 3. All complexes were characterized by C, H, N, Cl and Pt elemental analyses, FAB ϩ mass-spectrometry, IR and 1 H, 13 C{ 1 H} and 195 Pt NMR spectroscopies, and 2 and 3 by X-ray crystallography which indicates the chelating bidentate ligand adopts the nitroso form.

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