Cycloplatination of aryl and ferrocenyl oximes by cis-[PtCl2(OSMe2)(2)] affording expected platinum(II) and unexpected platinum(IV) products

Acetophenone, benzamide, ferrocenyl methyl ketone and ferrocenecarboxamide oximes reacted with cis-[PtCl2-(dmso)(2)] (dmso = dimethyl sulfoxide) in refluxing methanol to afford the expected platina(II)cycles N,S-trans-[Pt(C-N)CI(dmso)], where C-N stands for the corresponding cycloplatinated organic ligand. The highest yield : of 51% was observed in the case of the acetophenone oxime complex. The structures of the complexes were established on the basis of analytical and H-1 NMR data, and confirmed by an X-ray diffraction analysis of the platinated ferrocenyl methyl ketone oxime. A cyclic voltammetry study of the latter indicated that cyclometallation decreases the redox potential of the ferrocene unit by ca. 200 mV. The reaction of a bulkier analog of acetophenone oxime, viz. 2-methyl-1-phenylbutan-1-one oxime, resulted in the formation of the unexpected platinum(rv) complex fac-[Pt(C-N)Cl-3(SMe2)] revealing a unique combination of oxidative cycloplatination and dmso-deoxygenation processes which occur under rather mild conditions The composition of the platinum(Iv) : compound was established by X-ray crystallography. The Pt-CI bond distance trans to the phenyl carbon [2.464(4) Angstrom] is rather large. As a result, the trans chloro ligand undergoes rapid solvolysis in aqueous solution, causing a pH drop. The deoxygenation of dimethyl sulfoxide that occurs within the metal co-ordination sphere can be viewed as a model of the action of the metal-dependent redox enzyme dimethyl sulfoxide reductase.