The [(COD)M(R)] 14 VE complex fragments (COD = 1,5-cyclooctadiene, R = methyl or neopentyl (2,2-dimethylpropyl), M = Pd or Pt) bind to the nucleobases cytosine (Cyt) or uracil (Ura), to the methylated nucleobase derivatives 1-methylcytosine (1MeCyt) or 1-methyluracil (1MeUra), and to the related ligand caffeine (Caf) (1,3,7-trimethylxanthine). From the potentially bridging cytosinate ligand a binuclear platinum complex [(COD)(Me)Pt(N3-cytosinate-N1)Pt(Me)-(COD)] + was obtained. The solubility of the corresponding complexes in organic solvents allowed their characterization by multiple ( 1 H, 13 C, and 195 Pt) NMR spectroscopy and in some cases by crystal structure analysis. Relative ligand-metal bond strength were discussed in view of 1 H-195 Pt NMR coupling constants. Further focus lies on the observation of binding isomers, the formation of binuclear species, multiple substitution, and the observed differences between Pt and Pd derivatives. Cytotoxicity experiments on HT-29 colon carcinoma and MCF-7 breast cancer cell lines revealed promising activities for selected platinum COD complexes.

The occurrence of cis or trans configurations in square planar diarylbis(dimethyl sulfoxide)platinum(II) complexes with S-bonded dmso ligands and aryl = 2,3,4,5,6-pentamethylphenyl, 2,4,6-trimethylphenyl, 2,6-dimethylphenyl, 2-, 3-, and 4-methylphenyl, and phenyl has been investigated by multinuclear (1H, 13C, and 195Pt) NMR spectroscopy and crystal structure analysis. Both methods confirm the cis configuration for complexes with the smaller phenyl and methylphenyl (tolyl) ligands and the trans configuration for the compounds with the bulkier ligands, starting from 2,6-dimethylphenyl. Spectroscopic criteria could thus be established to identify configurational isomers. For the 2-tolyl complex an additional kind of isomerism arises from the relative orientation of the two methyl substituents on the same side (syn) or on different sides of the coordination plane (anti). 2D-NMR spectroscopy allowed us to identify the conformers and to study isomerization mechanisms. DFT calculation results agree well with the experimental structures and with the spectroscopic data.

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