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 K-2[PtCl4] with pyrimidine-2-thiol (pymSH) was reinvestigated. Among the possible four isomers, the major product was the cis isomer of [(Pt2Cl2)-Cl-III(pymS)(4)] (1). The Pt(II) complex cis-[Pt-2(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 K-2[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.