From Simpletrans-[a₂Pt(2-hydroxypyrimidine)₂]²⁺(a = NH₃, CH₃NH₂) Complexes to Structures of Higher Complexity. Molecular Recognition of 2-Aminopyrimidine by Hydrogen Bond Formation and Reactivity toward Additional Metal Ions

Abstract

The new complexes trans-[a2Pt(Hpymo-N1)2]X2 (a = NH3, X = NO3 (1a); a = CH3NH2, X = NO3 (1b); a = CH3NH2, X = ClO4 (1c); Hpymo = 2-hydroxypyrimidine) have been prepared by reaction of trans-[a2Pt(H2O)2]-X2 with 2-hydroxypyrimidine at 80 degrees C in water. Complex 1c cocrystallizes in water with 2-aminopyrimidine (ampym) through formation of complementary pairs of hydrogen bonds to give the supramolecular hexagon [trans-[(CH3NH2)2Pt(pymo-N1)(Hpymo-N1)].Hampym[2(ClO4)4 (2). Molecular recognition of ampym by 1c is responsible for a conformational change of the two hydroxypyrimidine ligands in 1c from anti (1c) to syn and in addition for a proton transfer from a Hpymo residue to ampym against 1.5 units of pKa gradient. 1H NMR concentration-dependent studies as well as NOE experiments in dmso-d6 and dmf-d7 show that 2 dissociates in solution. Compound 1a reacts in NH3:H2O (1:3) with AgI to give the polymeric species [trans-[(NH3)2Pt(mu-pymo-N1,N3)2Ag(H2O)]-NO3]n (3). In contrast to 2, in the polymeric structure the trans-[NH3)2Pt(pymo)2] entities adopt an anti conformation. Nevertheless, the [(H2O)Ag(pymo)2] residues present a syn conformation that leads to a meander-like global structure. Compounds 1b, 1c, 2, and 3 have been studied by X-ray crystallography: (1b) triclinic space group, P1, a = 9.300(2) A, b = 10.483(2) A, c = 11.050(2) A, alpha = 68.21(3) degrees, beta = 75.47(3) degrees, gamma = 73.83(3) degrees, Z = 2, R1 = 0.025, and wR2 = 0.062; (1c) triclinic space group, P1, a = 5.692(1) A, b = 7.758(2) A, c = 11.236(2) A, alpha = 93.12(3) degrees, beta = 92.86(3) degrees, gamma = 102.58(3) degrees, Z = 2, R1 = 0.048, and wR2 = 0.119; (2) triclinic space group, P1, a = 8.355(2) A, b = 11.221(2) A, c = 13.004(3) A, alpha = 86.76(3) degrees, beta = 78.62(3) degrees, gamma = 77.96(3) degrees, Z = 2, R1 = 0.033, and wR2 = 0.080; (3) monoclinic space group, C2/c, a = 5.345(1) A, b = 23.998(5) A, c = 12.474(2) A, beta = 102.27(3) degrees, Z = 8, R1 = 0.041, and wR2 = 0.093.

Ligand‐pKa Shifts through Metals: Potential Relevance to Ribozyme Chemistry

“…Again, metal ion coordination could assist H þ transfer between two different nucleobases, e.g., from guanine to adenine, by acidifying the N(1)H of guanine. At least in a model system containing a platinated pyrimidin-2-one ligand and a 2-aminopyrimidine, such a H-atom transfer against a pK a gradient has been observed by us [94].…”

Association Patterns of Platinated Purine Nucleobases in Metal-Modified Pairs and Triples

“…1 H NMR spectra were recorded on a Varian Mercury 200 FT NMR spectrometer or on a Varian Inova AS600, respectively. Sodium 3-(trimethylsilyl)propanesulfonate (TSP; δ ) 0.00 ppm) was used as an internal standard in aqueous solutions, while spectra recorded in DMSO-d 6 were calibrated to the signal of partially nondeuterated solvent. Spectra recorded in DMF-d 7 were likewise referenced against solvent peaks.…”

“…The assignment of the individual 1 H NMR resonances of 1a in DMSO-d 6 The terminal guanine base opposite to N1 of adenine adopts a head-tail orientation with respect to the latter, while the guanine across N7 of the central adenine is oriented in a way that a head-head arrangement results. A concentration dependence of 1a in DMSO-d 6 was carried out in the range 0.2-60 mM in order to investigate whether any self-association of 1a is taking place.…”

Crystallographic and structural characterization of heterometalic platinum complexes Part X. Heteropolynuclear pt complexes

“…2). The Pt-Ag bond distances (cis-vs trans-) are 2.897 (1) In polymeric trans-[(NH 3 ) 2 Pt(µ-pymo) 2 Ag(H 2 O)]NO 3 [25] the trans {(NH 3 ) 2 . Pt(pymo) 2 } moiety adopts an anticonformation.…”