Syntheses and structures of mono- and dinuclear platinum complexes of pyrimidine-2-thiolate and its 4-methyl and 4,6-dimethyl derivatives

The reaction of K₂[PtCl₄] with pyrimidine-2-thiol (pymSH) was reinvestigated. Among the possible four isomers, the major product was the cis isomer of [pt^III₂Cl₂(pymS)₄] (1). The Pt(II) complex cis-[Pt₂(pymS)₄] (2) was prepared by the addition of NaOCH₃ in the reaction mixture. The substitution of the axial Cl^- ligands of 1 with Br^- afforded the bromo complex [Pt₂Br₂(pymS)₄] (3). While the reactions of K₂[PtCl₄] with 4-methylpyrimidine-2-thiol hydrochloride (4-mpymSH·HCl) in the presence of NaHCO₃ gave a mixture of [Pt₂Cl₂(4-mpymS)₄] (4) and trans-[Pt(4-mpymS)₂] (5), the reaction with 4,6-dimethylpyrimidine-2-thiol (4,6-dmpymSH) gave only trans- [Pt(4,6-dmpymS)₂] (7). The preference of bis-chelate mononuclear complexes for these ligands may be explained by considering steric hindrance between the ligands in the dimer. The oxidation of 5 by Ce(IV) afforded trans-dichloro Pt(IV) complex, [PtCl₂(4-mpymS)₂] (6). The crystal structures of 1, 3, 6 and 7 were determined. The redox properties of 1 and 3 are also discussed.