Chlorination of Platinum-Bound Salicylaldoxime. The First Example of a Structurally Characterized Monodentate Salicylaldoxime-Type Ligand

Abstract

The reaction of K2[PtCl4] and salicylaldoxime in an approximate 1:2 molar ratio in water resulted in the isolation of a mixture of four compounds from which [Pt(o-OC6H4CH=NOH)2] (1) and [PtCl(OC6H4CH=NOH)(HOC6H4CH=NOH)] (2) were isolated, whereas the other two were shown to be unstable and decomposed both in solution and on SiO2 during chromatography. Chlorination of 1 and 2 with Cl2 resulted in the oxidative addition of chlorine to the platinum(II) center and in the chlorination of the benzene ring, giving the platinum(IV) complexes [PtCl2(3,5,2-Cl,Cl,OC6H2CH=NOH)2] (3) and [PtCl3(3,5,2-Cl,Cl,OC6H2CH=NOH)(3,5,2-Cl,Cl,HOC6H2CH=NOH)] (5), respectively, containing commercially unavailable 3,5-dichloro-2-hydroxybenzaldehye oxime. Alternatively, treatment of 1 with NOCl resulted only in the oxidation of the platinum(II) center to furnish [PtCl2(o-OC6H4CH=NOH)2] (4), whereas the benzene rings of salicylaldoximato ligands remained intact. All complexes were characterized by C, H, N, Cl and Pt elemental analyses, FAB+ mass spectrometry, IR and 1H, 13C{1H} and 195Pt NMR spectroscopy. Compounds 1, 3 and 5 were analyzed by X-ray crystallography. In 1, the salicylaldoximato ligands adopt a trans configuration and the hydrogen atoms of the OH groups are involved in intramolecular hydrogen bonding, forming five-membered rings. In 3, every molecule of the complex forms the repeating unit for a self-assembly that produces infinite one-dimensional polymeric chains directed along the z axis held by hydrogen bonds. The complex 5 represents the first example of a structurally characterized metal complex with a monodentate salicylaldoxime-type ligand, although the conventional bidentate N,O-coordination mode is a classical topic in coordination chemistry.