Complexes of Platinum(II) Containing Neutral and Deprotonated 9-Methyladenine. Synthesis, X-ray Structures, and NMR Studies on the Cyclic Trimer cis-[L₂Pt{9-MeAd(−H)}]₃(NO₃)₃ and the Dinuclear cis-[L₂Pt(ONO₂){9-MeAd(−H)}PtL₂](NO₃)₂ (L = PMePh₂)

Abstract

The dinuclear hydroxo complex cis-[L(2)Pt(mu-OH)](2)(NO(3))(2) (L = PMePh(2), 1), in CH(2)Cl(2), CH(3)CN, or DMF solution, deprotonates the NH(2) group of 9-methyladenine (9-MeAd) to give the complex cis-[L(2)Pt[9-MeAd(-H)]](3)(NO(3))(3), 2, which was isolated in good yield. The X-ray structure shows that the nucleobase binds symmetrically the metal centers through the N(1),N(6) atoms forming a cyclic trimer with Pt...Pt distances in the range 5.202(1)-5.382(1) A. Dissolution of 2 in DMSO or DMF determines the partial (or total) dissociation of the cyclic structure to form several fragments. A multinuclear NMR analysis of the resulting mixture supports the presence of the mononuclear species cis-[L(2)Pt[9-MeAd(-H)]](+), 3, in which the deprotonated nucleobase chelates the metal center with the N(6),N(7) atoms. Addition of a stoichiometric amount of the nitrato complex cis-[L(2)Pt(ONO(2))(2)] (L = PMePh(2), 4) to a DMSO or DMF solution of 2 affords quantitatively the diplatinated compound cis-[L(2)Pt(ONO(2))[9-MeAd(-H)]PtL(2)](NO(3))(2), 5. The single-crystal X-ray analysis shows that the adenine behaves as a tridentate ligand bridging two cis-L(2)Pt units at the N(1) and N(6),N(7) sites, respectively [Pt(1)-N(1) = 2.109(5) A, Pt(2)-N(6) = 2.095(7) A, Pt(2)-N(7) = 2.126(7) A]. The N(1)-bonded metal center completes the coordination sphere through an oxygen atom of a nitrate group, and its coordination plane is arranged orthogonally with respect the second one. The Pt-O distance [2.109(5) A] is similar to those found in the nitrato complex 4 [2.110 A, average]. The related complex cis-[[L(2)Pt(ONO(2))](2)(9-MeAd)](NO(3))(2), 6, containing the neutral adenine platinated at the N(1),N(7) atoms, was isolated and its stability in solution investigated by NMR spectroscopy. In DMSO, 6 undergoes decomposition forming a mixture of the species 4, 5, and the adenine mono- and bis-adducts cis-[L(2)Pt(9-MeAd)(DMSO)](2+), 7, and cis-[L(2)Pt(9-MeAd)(2)](2+), 8, respectively. This last complex, quantitatively formed upon addition of 9-MeAd (Pt/adenine = 1:2) to the mixture, was also isolated and characterized.

Synthesis and characterization of cis-[(PPh3)2Pt{9-MeAd(-H),N6N7}]X (X−= NO3, PF6): The first example of a platinum(II) complex containing the N6,N7-chelated 9-methyladenine anion

“…100 Hz). A better resolution of this resonance was found in DMSO-d 6 , as shown in Fig. 2 195 Pt satellites and these data are collected as shown in Table 2.…”

“…The 195 Pt resonance, at d À4948, in addition to the coupling with the 31 P nuclei, appears in resonance with the proton at d 4.507, with 2 J PtH = 105 Hz. The coordination mode of the 9-substituted adenine found in 2, structurally authenticated in Ru, Mo, Ir and Rh complexes [9][10][11][12][13][14], has only a few precedents in the Pt chemistry [7]. We have monitored the condensation reaction between the hydroxo complex 1 and 9-MaAd in a variety of solvents.…”

“…mass spectrometry. This binding mode of the adeninate ion has been previously described only for Mo(IV) [9], Rh(III) [10,11], Ir(III) [12] and Ru(II) [13,14] 15 N. Inverse detected spectra were obtained through heteronuclear multiple bond correlation (HMBC) experiments, using parameters similar to those previously reported [6]. ESI-MS spectra were performed with a MSD SL Trap mass spectrometer (Agilent Technologies, Palo Alto, CA, USA) operating in positive ion mode from m/z 100-2200.…”

“…In this contest, we have shown that the reaction of the hydroxo complexes cis-[L 2 Pt(l-OH)] 2 -(NO 3 ) 2 (L = tertiary phosphine) with 9-substituted adenines affords the polynuclear cyclic species cis-[L 2 Pt{adenine(-H),N 1 N 6 }] n (NO 3 ) n in which the NH 2 -deprotonated nucleobases bridge selectively the metal centres through the N(1) and N(6) atoms. The nuclearity of the adeninate complexes appears to be dependent on the nature of the neutral ligands L. PMe 3 stabilizes the dinuclear species (n = 2 [4,5]), while the trinuclear analogues (n = 3) are formed when L are PMe 2 Ph [6] and PMePh 2 [7]. With the latter phosphine the cation cis-½ðPMePh 2 Þ 2 Ptf9-MeAdðÀHÞ; N 1 N 6 g 3 3þ is stable only in chlorinated solvents.…”

“…With the latter phosphine the cation cis-½ðPMePh 2 Þ 2 Ptf9-MeAdðÀHÞ; N 1 N 6 g 3 3þ is stable only in chlorinated solvents. In fact, when dissolved in DMSO or DMF, it immediately converts into a complex mixture of products, among them the mononuclear derivative cis-[(PMePh 2 ) 2 Pt{9-MeAd(-H),N 6 N 7 }] + in which the nucleobase acts as a chelating ligand through the N(6) and N(7) atoms [7].…”