Titelbild: Fünfkernige Platin( II )‐Makrocyclen mit Nucleobasen (Angew. Chem. 10/2004)

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.

Section: Introductionmentioning

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

“…In this study we have demonstrated that the "directed" assembly of metallacalix [4]arenes containing the parent pyri- midine nucleobase cytosine also occurs when a cis-[Pt-…”

Section: Discussionmentioning

confidence: 97%

“…[2] The cations of cis- Figures 14 and 15, respectively. The molecular metallacalix [4]arene skeleton formed Scheme 3. Relationship between mononuclear 1, tetranuclear 5, and octanuclear 6 and 7.…”

Section: Inverting Metals Inmentioning

confidence: 99%

“…To this mixed metallacalix [4]arene scaffold pairs of (bpy)Pd II units are located above and below the N3-bonded (bpy)Pd II , linked through the deprotonated N4 and O2 sites of the cytosine bases. Consequently, the cytosine nucleobases in 6 are dianions (C 2À ).…”

Section: Isolation Of the Pt 2 Pd 6 Complex Cis-[{(nhmentioning

confidence: 99%

“…Table 1 lists structurally characterized multinuclear metal complexes of pym nucleobases that can be derived from metallacalix[n]arene structures with n = 3 and 4. [3][4][5][6][7] The complexity of the so-called "platinum pyrimidine blues", [8] a class of compound once considered the second generation of platinum antitumor drugs after Cisplatin, is possibly closely related to this propensity.…”

Section: The Linkage Isomer Of 5 Cis-[{pta C H T U N G T R E N N U Nmentioning

confidence: 99%

See 2 more Smart Citations

“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.

Mixed‐Metal (Platinum, Palladium), Mixed‐Pyrimidine (Uracil, Cytosine) Self‐Assembling Metallacalix[n]arenes: Dynamic Combinatorial Chemistry with Nucleobases and Metal Species

Bardají

Freisinger

Costisella

et al. 2007

Reactions between the mononuclear mixed-nucleobase complex [Pt(en)(UH-N1)(CH2-N3)]+ (1; en: ethylenediamine; UH-N1: uracil monoanion bonded through the N1 atom; CH2-N3: neutral cytosine bonded through the N3 atom) and [Pd(II)(en)] or [Pd(II)(2,2'-bpy)] (2,2'-bpy: 2,2'-bipyridine) lead to libraries of compounds of different stoichiometries and different connectivities. In these compounds, the palladium entity binds to or cross-links either the N3 sites of uracil and/or the N1 sites of cytosine, following deprotonation of these positions to give uracil dianions (U) and cytosine monoanions (CH). Cyclic species, which can be considered as metallacalix[n]arenes, have been detected in several cases, with n being 4 and 8. The complexity of the compounds formed not only results from the possibility of the two different nucleobases in building block 1 engaging in different connectivities with the Pd entities, but also from the potential for the formation of oligomers of different sizes and different conformations; in the case of cyclic tetranuclear Pt(2)Pd(2) species, this can, in principle, lead to the various arrangements (cone, partial cone, 1,2-alternate, 1,3-alternate) known from calix[4]arene chemistry. A further complication arises from the fact that, depending on the mutual orientation of the exocyclic groups of the two nucleobases (O2 and O4 of uracil, O2 and N4 of cytosine), these sites can be engaged in additional chelation of [Pd(II)(en)] and [Pd(II)(2,2'-bpy)]. Thus, penta-, hexa-, and octanuclear complexes, Pt(2)Pd(3), Pt(2)Pd(4), and Pt(2)Pd(6), derived from cyclic Pt(2)Pd(2) tetramers have been isolated and characterized.