cis ‐ and trans ‐Dichlorodiammineplatinum(II)

Pyrimidine (pym) ligands with their two endocyclic N-donor atoms provide 120° angles for molecular constructs, which, with the 90° angle metal fragments cis-a(2)M(II) (M=Pt, Pd; a=NH(3) or a(2)=diamine), form cyclic complexes known as metallacalix[n]arenes (with n=3, 4, 6, 8, …). The number of possible isomers of these species depends on the symmetry of the pym ligand. Although highly symmetrical (C(2v)) pym ligands form a single linkage isomer for any n and can adopt different conformations (e.g., cone, partial cone, 1,3-alternate, and 1,2-alternate in the case of n=4), low-symmetry pym ligands (C(s)) can produce a higher number of linkage isomers (e.g., four in the case of n=4) and a large number of different conformers. In the absence of any self-sorting bias, the number of possible species derived from a self-assembly process between cis-a(2)M(II) and a C(s)-symmetrical pym ligand can thus be very high. By using the C(s)-symmetric pym nucleobase cytosine, we have demonstrated that the number of feasible isomers for n=4 can be reduced to one by applying preformed building blocks such as cis-[a(2)M(cytosine-N3)(2)](n+) or cis-[a(2)M(cytosinate-N1)(2)] (for the latter, see the accompanying paper: A. Khutia, P. J. Sanz Miguel, B. Lippert, Chem. Eur. J. 2011, 17, DOI: 10.1002/chem.2010002723) and treating them with additional cis-a(2)M(II) . Moreover, intramolecular hydrogen-bonding interactions between the O2 and N4H(2) sites of the cytosine ligands reduce the number of possible rotamers to one. This approach of the "directed" assembly of a defined metallacalix[4]arene is demonstrated.

“…cis-[PtCl 2 A C H T U N G T R E N N U N G (NH 3 ) 2 ], [28] [PtCl 2 (en)], [29] and [PdCl 2 (en)] [30] were prepared as described in the literature. …”

Section: Methodsmentioning

confidence: 99%

“Directed” Assembly of Metallacalix[n]arenes with Pyrimidine Nucleobase Ligands of Low Symmetry: Metallacalix[n]arene Derivatives ofcis‐[a₂M(cytosine‐N3)₂]²⁺(M=Pt^II, Pd^II;n=4 and 6)

Khutia

Miguel

Lippert

2011

“…The following compounds were prepared as described in the literature: [Pt-A C H T U N G T R E N N U N G (dien)I]I, [44] [PtA C H T U N G T R E N N U N G (dien)Cl]Cl, [45] trans-[PtA C H T U N G T R E N N U N G (NH 3 ) 2 Cl 2 ], [46] trans-[Pt-A C H T U N G T R E N N U N G (MeNH 2 ) 2 Cl 2 ], [47] [Pd(en)Cl 2 ], [48] [PtA C H T U N G T R E N N U N G (NH 3 ) 3 Cl]Cl, [49] and [PtA C H T U N G T R E N N U N G (dien)(9-MeGH-N7)]A C H T U N G T R E N N U N G (ClO 4 ) 2 .…”

Section: Methodsmentioning

confidence: 99%

Pt^II Coordination to N1 of 9‐Methylguanine: Why it Facilitates Binding of Additional Metal Ions to the Purine Ring

Müller¹,

Shen²,

Miguel³

et al. 2011

The preparation and X-ray crystal structure analysis of {trans-[Pt(MeNH(2))(2)(9-MeG-N1)(2)]}⋅{3 K(2)[Pt(CN)(4)]}⋅6 H(2)O (3 a) (with 9-MeG being the anion of 9-methylguanine, 9-MeGH) are reported. The title compound was obtained by treating [Pt(dien)(9-MeGH-N7)](2+) (1; dien=diethylenetriamine) with trans-[Pt(MeNH(2))(2)(H(2)O)(2)](2+) at pH 9.6, 60 °C, and subsequent removal of the [(dien)Pt(II)] entities by treatment with an excess amount of KCN, which converts the latter to [Pt(CN)(4)](2-). Cocrystallization of K(2)[Pt(CN)(4)] with trans-[Pt(MeNH(2))(2)(9-MeG-N1)(2)] is a consequence of the increase in basicity of the guanine ligand following its deprotonation and Pt coordination at N1. This increase in basicity is reflected in the pK(a) values of trans-[Pt(MeNH(2))(2)(9-MeGH-N1)(2)](2+) (4.4±0.1 and 3.3±0.4). The crystal structure of 3 a reveals rare (N7,O6 chelate) and unconventional (N2,C2,N3) binding patterns of K(+) to the guaninato ligands. DFT calculations confirm that K(+) binding to the sugar edge of guanine for a N1-platinated guanine anion is a realistic option, thus ruling against a simple packing effect in the solid-state structure of 3 a. The linkage isomer of 3 a, trans-[Pt(MeNH(2))(2)(9-MeG-N7)(2)] (6 a) has likewise been isolated, and its acid-base properties determined. Compound 6 a is more basic than 3 a by more than 4 log units. Binding of metal entities to the N7 positions of 9-MeG in 3 a has been studied in detail for [(NH(3))(3)Pt(II)], trans-[(NH(3))(2)Pt(II)], and [(en)Pd(II)] (en=ethylenediamine) by using (1)H NMR spectroscopy. Without exception, binding of the second metal takes place at N7, but formation of a molecular guanine square with trans-[(Me(2)NH(2))Pt(II)] cross-linking N1 positions and trans-[(NH(3))(2)Pt(II)] cross-linking N7 positions could not be confirmed unambiguously, despite the fact that calculations are fully consistent with its existence.

“…cis-[PtCl 2 A C H T U N G T R E N N U N G (NH 3 ) 2 ], [24] [PtCl 2 (en)], [25] [PdCl 2 (en)], [26] [PdCl 2 A C H T U N G T R E N N U N G (2,2'-bpy)], [26] sodium cytosinate, [27] (600 mg, 2 mmol) and AgNO 3 (665 mg, 3.91 mmol) in DMF (30 mL) was stirred at room temperature for 40 h with light excluded. The resultant AgCl was filtered off through a bed of Celite, sodium cytosinate (525 mg, 3.95 mmol) was added, and the mixture was stirred at room temperature for three days.…”

Section: Methodsmentioning

confidence: 99%

“Directed” Assembly of Metallacalix[n]arenes with Pyrimidine Nucleobase Ligands of Low Symmetry: Interchanging Metals in Mixed‐Metal Metallacalix[4]arenes and Incorporating Additional Metals at the Exocyclic Groups

Khutia

Miguel

Lippert

2011

The pyrimidine (pym) nucleobase cytosine (H2C) forms cyclic ring structures (“metallacalix[n]arenes”) when treated with square‐planar cis‐a2MII entities (M=Pt, Pd; a=NH3 or a2=diamine). The number of possible linkage isomers for a given n and the number of possible rotamers can be substantially reduced if a “directed” approach is pursued. Hence, two cytosine ligands are bonded in a defined way to a kinetically robust platinum corner stone. In the accompanying paper (Part I: A. Khutia, P. J. Sanz Miguel, B. Lippert, Chem. Eur. J. 2010, 17, DOI: 10.1002/chem.2010002722) we have demonstrated this principle by allowing cis‐[Pta2(H2C‐N3)2]2+ to react with (en)PdII to give cycles of (N1,N3⋅N3,N1▪)x (with x=2 or 3; ⋅ represents PtII and ▪ represents PdII). In an extension of this work we have now prepared cis‐[Pta2(HC‐N1)2] (1; HC=monoanion of cytosine) and treated it with (bpy)PdII (bpy=2,2′‐bipyridine) to give the Pt2Pd2 cycle cis‐[{Pt(NH3)2(N1‐HC‐N3)2Pd(bpy)}2](NO3)4⋅13H2O (5) with the coordination sites of the metals inverted; hence, platinum is bonded to N1 and palladium is bonded to N3 sites. Again, not only the expected single linkage isomer is formed, but at the same time the solid‐state structure and 1H NMR spectroscopy reveal the preferential occurrence of a single rotamer (1,3‐alternate). The addition of (bpy)PdII to 5 led to the formation of Pd6Pt2 complex 6 in which the exocyclic N4H2 groups of the cytosine ligands have undergone deprotonation and chelate four more (bpy)PdII entities through the O2 and N4H sites. With a large excess of (bpy)PdII over 5 (4:1), cis‐(NH3)2PtII is eventually substituted by (bpy)PdII to give the Pd8 complex 7. In both 6 and 7 stacks of three (bpy)PdII entities occur. The linkage isomer of 5, cis‐[{Pt(NH3)2(N3‐HC‐N1)2Pd(bpy)}2](NO3)4⋅9H2O (8), has been structurally characterized and the two complexes compared. The acid/base properties of cis‐[Pt(NH3)2(H2C‐N1)2] (1) have been determined and compared with those of the corresponding N3 isomer. The complexation of AgCl by 1 is reported.