title: Mono- and polynuclear complexes of the model nucleobase 1-methylcytosine. Synthesis and characterization of cis-[(PMe2Ph)2Pt{(1-MeCy(-H)}]3(NO3)3 and cis-[(PPh3)2Pt{1-MeCy(-H)}(1-MeCy)]NO3.
abstract: The hydroxo complex cis-[L2Pt(mu-OH)]2(NO3)2 (L = PMe2Ph), in various solvents, reacts with 1-methylcytosine (1-MeCy) to give as the final product the cyclic species cis-[L2Pt{1-MeCy(-H),N 3N 4}]3(NO3)3 (1) in high or quantitative yield. X-ray analysis of 1 evidences a trinuclear species with the NH(2)-deprotonated nucleobases bridging symmetrically the metal centers through the N3 and N4 donors. A multinuclear NMR study of the reaction in DMSO-d6 reveals the initial formation of the dinuclear species cis-[L2Pt{1-MeCy(-H),N 3N 4}]2(2+) (2), which quantitatively converts into 1 following a first-order kinetic law (at 50 degrees C, t(1/2) = 5 h). In chlorinated solvents, the deprotonation of the nucleobase affords as the major product (60-70%) the linkage isomer of 1, cis-[L2Pt{1-MeCy(-H)}]3(3+) (3), in which three cytosinate ligands bridge unsymmetrically three cis-L2Pt(2+) units. In solution, 3 slowly converts quantitatively into the thermodynamically more stable isomer 1. No polynuclear adducts were obtained with the hydroxo complex stabilized by PPh3. cis-[(PPh3)2Pt(mu-OH)]2(NO3)2 reacts with 1-MeCy, in DMSO or CH2Cl2, to give the mononuclear species cis-[(PPh3)2Pt{1-MeCy(-H)}(1-MeCy)](NO3) (4) containing one neutral and one NH2-deprotonated 1-MeCy molecule, coordinated to the same metal center at the N3 and N4 sites, respectively. X-ray analysis and NMR studies show an intramolecular H bond between the N4 amino group and the uncoordinated N3 atom of the two nucleobases.
authors.affiliation: Istituto di Scienze e Tecnologie Molecolari, CNR, c/o Dipartimento di Scienze Chimiche, Università di Padova, Via Marzolo 1, 35131 Padova, Italy. bruno.longato@unipd.it
authors.forename: Bruno
authors.initials: B
authors.lastname: Longato
authors.forename: Diego
authors.initials: D
authors.lastname: Montagner
authors.forename: Ennio
authors.initials: E
authors.lastname: Zangrando
mesh_terms: D018360:Crystallography, X-Ray; D003596:Cytosine / Q000031:analogs & derivatives* / Q000737:chemistry; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D009944:Organoplatinum Compounds / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D009944:Organoplatinum Compounds; C031532:1-methylcytosine; D003596:Cytosine