PHOSPHINE ANALOGS OF CISPLATIN - SYNTHESIS AND X-RAY STRUCTURE OF BIS(MU-HYDROXO)BIS(BIS(TRIMETHYLPHOSPHINE)PLATINUM(II)) DINITRATE AND ITS REACTIVITY WITH 1-METHYLCYTOSINE - X-RAY STRUCTURE OF BIS(MU-1-METHYLCYTOSINATO-N3,N4)BIS(BIS(TRIMETHYLPHOSPHINE)PLATINUM(II)) DINITRATE

The complex cis-[(PMe3)2Pt(μ-OH)]2(NO3)2has been prepared and characterized by multinuclear 1H, 31P, and 195Pt NMR spectroscopy. The dimeric nature of the cationic complex found in solution has been confirmed in the solid state by single-crystal X-ray analysis. The compound crystallizes in the monoclinic system, space group P21/n with a = 15.511 (7) Å, b = 12.315 (5) Å, c = 6.964 (4) Å, β = 97.67 (4)°, and Z = 2. The structure was solved by heavy-atom methods and refined by least-squares techniques to R = 0.048 for 2748 unique data (I ≥ 3σ (I)). The cationic unit cis[(PMe3)2Pt(μ-OH)]22+contains bridging hydroxo ligands with the Pt atoms in a distorted square-planar geometry. The P-Pt-P and O-Pt-O angles are 95.4 (1) and 75.9 (4)°espectively. The P4Pt2O2skeleton is planar with a rather short O-O distance (2.54 (1) Å). The reaction of this complex with 1-methylcytosine (1-MeCy) has been investigated, in H2O and dimethyl sulfoxide (DMSO), by 31P NMR spectroscopy, cis [(PMe3)2Pt(0µ -OH)]22+reacts with the nucleobase, at room temperature in a few hours, with deprotonation of the exocyclic amino group and metal coordination of the cytosinate ligand. The main reaction product is the dinuclear complex cis-[(PMe3)2Pt(μ-l-MeCy(-H))]2(NO3)2, which has been characterized in solution by multinuclear NMR spectroscopy and in the solid state by single-crystal X-ray analysis. The complex crystallizes in the triclinic system, space group PI, with a = 10.320 (4) Å, b = 10.431 (5) Å, c = 17.426 (8) Å, ± = 92.39 (4)°, β = 99.13 (4)°, γ = 94.54 (5)°, and Z = 2. The structure was solved by heavy-atom: methods and refined to R = 0.038 for 5900 unique data (I ≥ 3σr(I)). The two deprotonated 1-MeCy molecules bridge two cis-(PMe3)2Pt moieties in a N3, N4head-to-tail fashion to form a dinuclear species in which the coordination planes of the two metal atoms form a dihedral angle of 46.2#x00B0;. At 80 °C, in H2O or DM;SO solution, the complex dissociates to the corresponding mononuclear species. The molecular structures and the solution state of the prepared complexes are discussed with reference to those of the amine analogues. © 1990, American Chemical Society. All rights reserved.