The dinuclear complexes cis-[(PMe3)2Pt(1-MeCy(-H))]2X2 (X = NO3- (1A), ClO4- (1B)), containing NH2-deprotonated 1-methylcytosine (1-MeCy(-H)) ligands, in aqueous or DMSO solution, at 80-degrees-C convert quantitatively into the corresponding trinuclear derivatives cis-[(PMe3)2Pt(1-MeCy(-H))]3X3(2A,B) which have been characterized in the solid state by single-crystal X-ray analysis and in solution by multinuclear (H-1, P-31, Pt-195, C-13, and N-15) NMR spectroscopy. The nitrate salt (2A) crystallizes from ethanol in the triclinic system, space group Pl. The crystals, stable only in the presence of the solvent, have the following cell dimensions: a = 13.542(5) angstrom, b = 17.352(5) angstrom, c = 20.721(6) angstrom, alpha = 113.13(2)degrees, beta = 104.30(3)degrees, gamma = 95.77(3)degrees, Z = 2. The structure, formulated as cis-[(PMe3)2Pt(1-MeCy(-H))]3(NO3)3.EtOH.H2O, was refined to R = 6.3 and R(w) = 6.3. Better structural data were obtained with the perchlorate derivative (2B), cis-[(PMe3)2Pt(1-MeCy(-H))]3(ClO4)3.2H2O, whose structure was refined to R = 4.4 and R(w) =4.9. The colorless prisms formed from aqueous solutions have the following crystallographic data: triclinic system, space group P1BAR, a = 14.634(7) angstrom, b = 14.791(9) angstrom, c = 14.980(9) angstrom, alpha = 101.93(5)degrees, beta = 103.46(5)degrees, gamma = 90.50(4)degrees, Z = 2. In both salts, the molecular structure of the cationic complex contains three cis-(PMe3)2Pt units linked to three 1-methylcytosine anions through the N(3) and N(4) atoms. The resulting 12-membered ring contains the pyrimidinic rings almost perpendicular to the plane defined by the metal atoms. Each platinum has a square-planar coordination with a Pt...Pt distance of 5.2A. The H-1, P-31, and C-13 NMR spectra indicate that the approximate S3 symmetry of the cation is maintained in solution. The compounds 1A and 2A were also characterized by N-15 NMR spectroscopy, at natural abundance. The spectroscopic data, obtained in DMSO-d6 solution, are compared with those of the derivative cis-[(PMe3)2Pt(1-MeCY)2](NO3)2 containing as ligands the neutral N(3)-bonded nucleobase. The dinuclear and trinuclear complexes exhibit very similar N-15 chemical shifts and 2J(PN) coupling constants but remarkably different from those of the mononuclear complex

The complex cis-[ (PMe3)2Pt(p-OH)]2(N03)z has been prepared and characterized by multinuclear 'H, 31P, and i95Pt 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 P 2 i / n , with a = 15.51 1 (7) A, b = 12.315 (5) A, c = 6.964 (4) A, p = 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 L 340). The cationic unit ~is-[(PMe,)~Pt(p-oH)]?' contains bridging hydroxo ligands with the Pt atoms in a distorted square-planar geometry. The P-Pt-P and 0-Pt-0 angles are 95.4 (1) and 75.9 (4)O, respectively. The P4Pt202 skeleton is planar with a rather short 0---0 distance (2.54 ( I ) A). The reaction of this complex with I-methylcytosine (I-MeCy) has been investigated, in H 2 0 and dimethyl sulfoxide (DMSO), by "P NMR spectroscopy. cis-[(PMe3)2Pt(pOH)]p 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-[(PMe,),Pt(p-I -MeCy(-H))],(NO,),, 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) A, b = 10.431 (5) A, c = 17.426 (8) A, CY = 92.39 (4)O, ( 3 = 99.13 (4)O, y = 94.54 (5)O, and Z = 2. The structure was solved by heavy-atommethods and refined to R = 0.038 for 5900 unique data ( I L 341)). The two deprotonated I-MeCy molecules bridge two cis-(PMe3),Pt moieties in a N3,N4 head-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'. At 80 'C, in H20 or DMSO 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.

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The dinuclear complex [(dppf)Pt(mu-OH)]2(BF4)2, where dppf is 1,1'-bis(diphenylphosphino)ferrocene, reacts with 1-methylthymine (1-MeTy), in dimethylformamide, dimethyl sulfoxide, or acetonitrile, to give the mononuclear complex [(dppf)Pt(1-MeTy(-H))(S)]+. The dimethylformamide adduct (S = DMF), [(dppf)Pt(1-MeTy(-H))(DMF)]BF4.CH2Cl2 (1), has been characterized by single-crystal X-ray analysis. The complex crystallizes in the orthorhombic system, space group P2(1)2(1)2(1), with a = 13.492 (3) angstrom, b = 14.063 (3) angstrom, c = 23.906 (4) angstrom, and Z = 4. The structure was solved by heavy-atom methods and refined by least-squares techniques to R = 0.078 for 2949 unique data (I > 3-sigma(I)). In the cationic unit, the ligand geometry around Pt is distorted square planar, the chelating bis(phosphine) dppf, the N(3)-bonded 1-methylthyminate and the O-bonded DMF ligands defining the coordination sphere of the metal ion. The 1-MeTy(-H) ring forms an angle of 104.8-degrees with the ligand square plane, while the DMF mean plane is at 73.0-degrees to the same plane. Addition of 1-methylcytosine (1-MeCy) to 1 affords the corresponding adduca [(dppf)Pt(1-MeTy(-H))(1-MeCy)]+ (2) as a mixture of two isomeric forms (2a,b). In solution at room temperature 2a extensively converts in 2b (90% in DMF) in several hours. Crystals of 2 are obtained from a chloroform solution of the two isomers and have been characterized by single-crystal X-ray analysis. They crystallize in the monoclinic system, space group C2/c, with a = 17.821 (5) angstrom, b = 21.718 (7) angstrom, c = 13.814 (3) angstrom, beta = 113.6 (2)-degrees, and Z = 4. The structure was solved by heavy-atom methods and refined by least-squares techniques to R = 0.060 for 2657 unique data (I > 3-sigma(I)). In the cationic complex [(dppf)Pt(1-MeTy(-H))(1-MeCy)]+ the platinum atom is coordinated by the chelated bis(phosphine), by the deprotonated 1-MeTy, and by the neutral 1-MeCy ligands. In 2 both the nucleobases are platinated at the N(3) site with their rings being perpendicular to the PtP2 plane. The structures in solution of the two isomers 2a and 2b are discussed on the basis of their H-1 and P-31 NMR spectra. Isomer 2b contains the neutral cytosine ligand coordinated to the platinum through the monodeprotonated exocyclic amino group, with the proton switched to the N(3) position. The conversion of 2a into 2b is consistent with the migration of the platinum from the N(3) to N(4) site of 1-MeCy indicating that the thermodynamically favored adduct of this neutral ligand is its imino oxo tautomeric form. In addition, the characterization of the species [(dppf)Pt(1-MeCy(-H))]+, obtained from [(dppf)Pt(mu-OH)]2(BF4)2 and 1-MeCy in acetonitrile, is described. On the basis of H-1 and P-31 NMR spectra, the complex appears to contain the deprotonated 1-MeCy chelated to the (dppf)Pt2+ moiety through its N(3) and N(4) donor atoms

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