REACTION OF MODEL NUCLEOBASES WITH THE DIAQUA(BIS(N-EMTHYLIMIDAZOL-2-YL) KETONE)PLATINUM(II) DICATION - SYNTHESIS AND STRUCTURE OF THE HEAD-TO-TAIL ISOMERS OF BIS(9-METHYLGUANINE-N7)(BIS(N-METHYLIMIDAZOL-2-YL) KETONE)PLATINUM(II) PERCHLORATE, BIS(1-METHYLCYTOSINE-N3)(BIS-(-METHYLIMIDAZOL-2-YL) KETONE)PLATINUM(II) PERCHLORATE, BIS(MU-1-METHYLTHYMINATO-N3,O4)BIS[BIS(N-METHYLIMIDAZOL-2-YL) KETONE)PLATINUM(II)] PERCHLORATE, AND BIS(MU-1-METHYLURACILATO-N3,O4)BIS[(BIS(N-METHYLIMIDAZOL-2-YL) KETONE)PLATINUM(II)] NITRATE

The reactions of [Pt(bmik)(H2O)2]+ (bmik = bis(N-methylimidazol-2-yl) ketone) with 9-methylguanine (9-MeGH), 1-methylcytosine (1-MeC), 1-methylthymine (1-MeTH), and 1-methyluracil (1-MeUH) were studied, and the products were characterized by X-ray structure analysis. The bmik diaqua complex reacts to mononuclear complexes with the bases 9-methylguanine and 1-methylcytosine like its cis-dichlorodiammineplatinum(II) (cis-DDP) analog. In contrast, it forms dinuclear ones with 1-methylthymine and 1-methyluracil. In the structure of [Pt(bmik)(9MeGH)2] (ClO4)2.2H2O (1, PtC21H24N14O11Cl2.2H2O, monoclinic, P2(1)/c, with cell dimensions of a = 8.345(2) angstrom, b = 29.800(5) angstrom, c = 13.232(3) angstrom, beta = 93.69(2)-degrees, Z = 4, and V = 3284(1) angstrom3) the platinum atom is coordinated by a bmik ligand and two 9-methylguanines via their N(7) nitrogen atoms. The two nucleobases are arranged head-to-tail as in the molecular cation of [Pt(bmik)(1-MeC)2] (ClO4)2.1.5H2O (2, PtC19H24N10O11Cl2.1.5H2O, triclinic, P1BAR, with cell dimensions of a = 7.507(2) angstrom, b = 12.483(3) angstrom, c = 17.177(5) angstrom, alpha = 109.26(2)-degrees, beta = 93.15(2)-degrees, gamma = 99.64(2)-degrees, Z = 2, and V = 1488(1) angstrom3). The metal atom is coordinated by the N(3) atom, and the head-to-tail arrangement of the 1-methylcytosine bases is stabilized by hydrogen bonds. A formation of dinuclear complexes was not observed. Dinuclear cations can be synthesized with 1-methylthymine and 1-methyluracil as nucleic acid model nucleobases: [Pt2(bmik)2(1-MeT)2](ClO4)2.5H2O (3, Pt2C30H34N12O14Cl2.5H2O, triclinic, P1BAR, with a = 12.258(3) angstrom, b = 13.491(3) angstrom, c = 15.332(3) angstrom, alpha = 78.04(2)-degrees, beta = 68.83(2)-degrees, gamma = 68.48(2)-degrees, Z = 2, and V = 2192(1) angstrom3) and [Pt2(bmik)2(1-MeU)2](NO3)2.2H2O (4, Pt2C28H30N14O12.2H2O, orthorhombic, Pbcn, with a = 13.877(4) angstrom, b = 11.884(3) angstrom, c = 21.970(5) angstrom, Z = 4, and V = 3622(1) angstrom3). The intramolecular Pt...Pt distances are 2.900(1) (3) and 2.841(1) angstrom (4). Both bases show a head-to-tail arrangement while the platinum atoms are coordinated by two additional bmik ligands. Oxidation of 2 and 3 to platinum blues with higher valent Pt was not observed, presumably because of the competing oxidation of the low-potential bmik ligand. This different redox behavior distinguishes the reaction properties of cis-DDP and Pt(bmik)Cl2 with nucleobases in a characteristic way. H-1 NMR data are reported for the complexes.