Synthesis and NMR characterization of the novel mixed-ligand Pt(II) complexes cis- and trans-Pt(Ypy)(pyrimidine)Cl 2 and trans, trans-Cl 2(Ypy)Pt(μ-pyrimidine)Pt(Ypy)Cl 2 (Ypy = pyridine derivative)

Abstract

Mixed-ligand complexes of the type cis- and trans-Pt(Ypy)(pm)Cl 2 where Ypy = pyridine derivative and pm = pyrimidine were synthesized and characterized by IR spectroscopy and by multinuclear ( 195Pt, 1H and 13C) magnetic resonance spectroscopy. The cis compounds were prepared from the reaction of K[Pt(Ypy)Cl 3] with pyrimidine (1:1 proportion) in water, while most of the trans isomers were synthesized from the isomerization of the cis compounds. The cis isomers could not be isolated with the Ypy ligands containing two –CH 3 groups in ortho positions. When the aqueous reaction of K[Pt(Ypy)Cl 3] with pyrimidine was performed in a Pt:pm ratio = 2:1, the pyrimidine-bridged dinuclear species were formed. Only the most stable trans– trans isomers could be isolated pure. In IR spectroscopy, the cis monomers showed two ν(Pt–Cl) bands, while the trans monomers and dimers showed only one ν(Pt–Cl) band. The 195Pt NMR signals of the cis monomers were found at slightly higher fields than those of the corresponding trans isomers. The δ( 195Pt) of the dimers were found close to those of the trans monomers. The NMR results were interpreted in relation to the solvent effect, which seems important in these complexes. The coupling constants J( 195Pt– 1H) and J( 195Pt– 13C) are larger in the cis geometry. The crystal structures of the compounds cis-Pt(2,4-lut)(pm)Cl 2, trans-Pt(2,6-lut)(pm)Cl 2 and trans, trans-Cl 2(2,6-lut)Pt(μ-pm)Pt(Ypy)Cl 2 were studied by X-ray diffraction methods and the results have confirmed the configurations suggested by IR and NMR spectroscopies.