Synthesis and NMR characterization of the novel mixed-ligands Pt(II) complexes Pt(amine)(pyrimidine)X2 and trans,trans-X2(amine)Pt(μ-pyrimidine)Pt(amine)X2 (X = I and Cl)

Mixed-ligand complexes of the type Pt(amine)(pm)I2, (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 I(amine)Pt(μ-I)2Pt(amine)I with pyrimidine (1:2 proportion) in water, while the trans isomers were synthesized from the isomerization of the cis complexes in acetone. The cis isomers could not be isolated with several amines, especially the more bulky ones. In 1H NMR, the pyrimidine protons of the cis compounds were found at lower fields than those of the trans analogs and the J(195Pt–1H) coupling constants are slightly larger in the cis geometry. For n-butylamine, the reaction produced also I2(n-butylamine)Pt(μ-pm)Pt(n-butylamine)I2. No such dimer could be isolated with the other amines. The compounds Pt(amine)(pm)Cl2 were also prepared (amine = methylamine and t-butylamine) from the ionic complex K[Pt(amine)Cl3] using an excess of pyrimidine. The IR and NMR characterization showed that the methylamine compound was a cis–trans mixture, while only the trans isomer was isolated with t-butylamine. When the same reaction was performed using a Pt:pm ratio of 2:1, Cl2(amine)Pt(μ-pm)Pt(amine)Cl2 was isolated. The pyrimidine-bridged dimers were identified by IR and multinuclear magnetic resonance spectroscopies as the trans–trans isomers. The trans monomers and dimers showed only one ν(Pt–Cl) band. The 195Pt NMR signals of the dimers were found close to those of the monomer trans-Pt(amine)(pm)Cl2.