[show abstract][hide abstract] ABSTRACT: A family of Pd(II) /Pt(II) dinuclear receptors, designed to give a smooth increase in their cavity lengths (from 7.46-13.78 Å), is presented. Their inclusion complexes with a representative set of polycyclic aromatic substrates (naphthalene, carbazol, pyrene, and benzo[a]pyrene), were characterized and studied in aqueous solution and the solid state. By taking into account the dimensions of both receptors and substrates, an excellent complementarity was found between the size of the receptors and their ability to complex a given substrate. Furthermore, this dimensional matching results in specific binding modes depending on the ability of the guest to establish stabilizing [CH⋅⋅⋅π] interactions with the host.
[show abstract][hide abstract] ABSTRACT: New inclusion complexes and catenanes were self-assembled from a fluorescent diazapyrenium based ligand, a PdII or PtII complex, and cyclic or acyclic electron rich aromatic guests in aqueous and organic media. The molecular rectangles display a π-deficient cavity suitable to incorporate π-donor aromatic systems. The inclusion complexes between the metallocycles and phenylenic (2a,b) and naphthalenic (3a,b–5a,b) derivatives were studied by NMR, UV-vis and fluorescence spectroscopy. The crystal structure of (3b) ⊂ 1a·6PF6 confirmed the insertion of the guest into the cavity of the metallocycle. Following the same self-assembly strategy, the use of polyethers 6,7 as π-donors resulted in the self-assembly of the catenanes 1a(6,7)·6PF6. Single-crystal X-ray analysis of 1a(7)·6PF6 revealed the catenane structure being stabilized by π-stacking and [C–HO] interactions.
[show abstract][hide abstract] ABSTRACT: New inclusion complexes and catenanes were self-assembled from a fluorescent diazapyrenium based ligand, a Pd(II) or Pt(II) complex, and cyclic or acyclic electron rich aromatic guests in aqueous and organic media. The molecular rectangles display a π-deficient cavity suitable to incorporate π-donor aromatic systems. The inclusion complexes between the metallocycles and phenylenic () and naphthalenic () derivatives were studied by NMR, UV-vis and fluorescence spectroscopy. The crystal structure of () ⊂ ·6PF(6) confirmed the insertion of the guest into the cavity of the metallocycle. Following the same self-assembly strategy, the use of polyethers , as π-donors resulted in the self-assembly of the catenanes (,)·6PF(6). Single-crystal X-ray analysis of ()·6PF(6) revealed the catenane structure being stabilized by π-stacking and [C-HO] interactions.
[show abstract][hide abstract] ABSTRACT: The interaction with native DNA of a 2,7-diazapyrenium-based ligand 1 and its Pt(II) rectangular metallacycle 2 is explored through circular and linear dichroism and fluorescence spectroscopies. The metal-free ligand 1 binds through intercalation, with a binding constant of approximately 5×10(5) M(-1), whereas the metallacycle 2 binds and bends the DNA with a binding constant of 7×10(6) M(-1). PCR assays show that metallo-supramolecular box 2 interferes with DNA transactions in vitro whereas the intercalator 1 does not. The metallacycle is active against four human cancer cell lines, with IC(50) values ranging between 3.1 and 19.2 μM and shows similar levels of efficacy, but a different spectrum of activity, to cisplatin.
[show abstract][hide abstract] ABSTRACT: An efficient microwave-assisted self-assembly of dinuclear platinum metallocycles is reported. The reactions proceed to afford the products with high purity and yields within 3-4 h. We have used this methodology to synthesize a new 14.75 Å × 14.75 Å molecular square. The solid-state structure showed a perfect alignment of the squares along the c axis.
[show abstract][hide abstract] ABSTRACT: New fluorescent square-shaped metallocycles were self-assembled from N-monoalkyl-2,7-diazapyrenium derivatives 1 and 4 and Pd(II)/Pt(II) complexes. Using ligand 1, the metal-directed self-assembly process produced a single metallocycle, while the non-symmetrical salt 4 produced mixtures of regioisomeric Pd(II) and Pt(II) metallocycles upon complexation with the corresponding square-planar cis-complexes. Due to the improved p-deficient character of 1 and 4 compared to related bipyridinium-based ligands, complexation and catenation of the obtained metallocycles with selected electron-rich aromatic substrates produced the corresponding 1 : 2 inclusion complexes and catenanes in a highly efficient fashion. This is particularly relevant for metallocycles derived from ligand 4, as complexation and catenation occurs in a regioselective fashion, generating only the supramolecules with the appropriate parallel arrangement of the diazapyrenium subunits in order to maximize the host-guest pi-stacking interactions. The potential of the new metallocycles for optical signalling applications is illustrated by analyzing their absorption and emission behaviour upon complexation and catenation.
Chemical Science 01/2011; 2:2407-2416. · 8.31 Impact Factor
[show abstract][hide abstract] ABSTRACT: New palladium and platinum metallacycles have been synthesized by reaction between a 2,7-diazapyrenium-based ligand and Pd(II) and Pt(II) complexes. The inclusion complexes between the metallacycles and polycyclic aromatic hydrocarbons (PAHs) in CD(3)NO(2) and D(2)O were studied by NMR spectroscopy. The structures of the inclusion complexes of the Pt metallacycle as host with pyrene, phenanthrene, and triphenylene were confirmed by single crystal X-ray crystallography. The association constants between the Pt metallacycle and the selected PAHs were determined in CH(3)CN following the characteristic charge-transfer band displayed in their UV/Vis absorption spectrum. Although in aqueous solution all the complexes showed a 1:1 stoichiometry, in CH(3)CN the Job plot indicated a 2:1 stoichiometry for complexes with triphenylene and benzo[a]pyrene. The estimated association constants in water correlate with the hydrophobicity of the PAH, indicating that hydrophobic forces play an important role in the complexation process.
[show abstract][hide abstract] ABSTRACT: Corner-connected molecular squares were self-assembled from a three-component system formed by a bidentate ligand and two palladium or platinum complexes. The system is dynamic and the constitution of the species in solution can be modulated under stoichiometric control.
Chemical Communications 09/2010; 46(36):6672-4. · 6.38 Impact Factor
[show abstract][hide abstract] ABSTRACT: A bidentate ligand based on N-monoaryl 4,4'-bipyridinium undergoes self-assembly to dinuclear rectangular metallocycles upon coordination to palladium(II) and platinum(II) centers. These metallocycles form a very stable complex with pyrene in aqueous solution and in the solid state. A crystal structure of the pyrene inclusion complex is presented. The association constants between pyrene and metallocycle 3a in organic solvents and water (K(a) = 2.3 x 10(6)) were determined.
[show abstract][hide abstract] ABSTRACT: The self-assembly of two new ligands based on the trans-1,2-bis(4-pyridyl)ethylene motif with palladium or platinum complexes led to quadrangular metallocycles. 1,1'-Methylenebis(4-((E)-2-(pyridin-4-yl)vinyl)pyridinium gave the square metallocycles, while the second ligand, which is less symmetrical, gave a mixture of the regioisomeric metallocyles. The metallocycles display the ideal disposition of the pi-acceptor units to maximize the pi-stacking interactions with aromatic guests. Thus, molecular recognition of pi-donor aromatic guests by square metallocycles produced the corresponding 2:1 inclusion complexes. On the other hand, starting from the mixture of regioisomers, the incorrect regioisomer rearranged to the correct metallocycle upon the addition of aromatic guests. On the basis of this behavior, a catenane was obtained regioselectively from the mixture of the regioisomeric metallocycles and the appropriate cyclophane. The formation of this catenane was confirmed by NMR and X-ray crystallographic studies.
The Journal of Organic Chemistry 10/2009; 74(17):6577-83. · 4.56 Impact Factor
[show abstract][hide abstract] ABSTRACT: Dinuclear metallocycles were assembled from an L-shaped bidentate ligand based on 4,4'-bipyridine and palladium or platinum square-planar cis complexes. The palladium (4a,b) or platinum (5a,b) square metallocycles were obtained as 1:1 regioisomeric mixtures depending on which pair of coordinative nitrogen atoms binds to the metal center. The squares display a pi-deficient cavity suitable to incorporate two pi-donor aromatic systems. Therefore, the reaction with macrocyclic polyethers (BPP34C10 or DN38C10) resulted in the regioselective self-assembly of the catenanes 4a(BPP34C10 or DN38C10)(2) x 6 PF(6) and 5a(BPP34C10 or DN38C10)(2) x 6 PF(6) because only macrocycles 4a and 5a present the correct disposition of the pi-deficient aromatic systems to maximize the pi...pi stacking interactions. Single-crystal X-ray analyses of catenanes revealed that the structures are additionally stabilized by [C-H...O], [N-H...O] bonds and [C-H...pi] interactions. The 1:2 inclusion complexes of metallocycles were prepared by self-assembly of three components: the ligand 1-(4-(pyridin-4-yl)benzyl)-4,4'-bipyridin-1-ium, a square planar complex M(en)(NO(3))(2) (M = Pd or Pt, en = ethylenediamine), and a dioxoaromatic guest in a 2:2:2 ratio. The comparative study of the formation of 1:2 inclusion complexes has allowed us to conclude that the pi...pi interactions between the host and guests are responsible for the observed regioselectivity.
[show abstract][hide abstract] ABSTRACT: The synthesis and the crystal structure of a doubly braided catenane, a new molecular Solomon link, obtained by a 5-component-self-assembly process based on coordinative bonds, pi-donor/pi-acceptor interactions, and hydrogen bonding is reported.
Journal of the American Chemical Society 01/2009; 131(3):920-1. · 10.68 Impact Factor
[show abstract][hide abstract] ABSTRACT: A new dinuclear Pd(II) metallocycle consisting of a 4,4'-bipyridin-1-ium ligand with a quinoline moiety was self-assembled in aqueous solution with the aid of template molecules; the situation found in solution in which both syn and anti or only the anti atropoisomers are observed strongly relies on the intermolecular host-guest interactions.
Chemical Communications 08/2008; · 6.38 Impact Factor
[show abstract][hide abstract] ABSTRACT: Two new 1:2 inclusion complexes were prepared by self-assembly of three components: a ligand based on 4,4'-bipyridinium, a square-planar Pd complex, and a dihydroxyaromatic guest (hydroquinone or 1,5-dihydroxynaphthalene) in a 2:2:2 ratio. Their X-ray structural analyses revealed that the complexes are stabilized by pi-pi stacking and [C-H...pi] interactions.
[show abstract][hide abstract] ABSTRACT: Dinuclear square metallocycles 3a,b assemble spontaneously when M(en)(OTf)2 (M = Pd, Pt) and a 4,4'-bipyridinium ligand are mixed in acetonitrile. Six new catenanes were prepared in good yields by thermodynamically driven self-assembly reaction of molecular squares 3a,b and pi-complementary dioxoaryl cyclophanes. Single-crystal X-ray analyses of the catenanes revealed the insertion of two aromatic units inside the metallocycle cavity. The structures are stabilized by means of a combination of pi-pi stacking, [C-H...pi] interactions, and [C-H...O] hydrogen bonds. Catenane (DB24C8)2-(3a) showed in solid-state two external DB24C8 rings positioned over the Pd(en) corners, which are held in position by [N-H...O] hydrogen bonds. Furthermore, formation of catenane (DB24C8)2-(3a) can be switched off and on in a controllable manner by successive addition of KPF6 and 18-crown-6.
Journal of the American Chemical Society 12/2007; 129(45):13978-86. · 10.68 Impact Factor
[show abstract][hide abstract] ABSTRACT: A metal-directed self-assembly of catenanes in combination with pi-pi interactions was investigated. Ligands based on 4,4'-bipyridinium or 2,7-diazapyrenium were used in conjunction with dioxoaryl cyclophanes (4-6) and trans-PdCl2(CH3CN)2. The catenanes show a dinuclear palladium 46-membered metallomacrocycle interlocked by two pi-complementary dioxoaryl macrocycles. [structure: see text].
[show abstract][hide abstract] ABSTRACT: New palladium and platinum metallocycles have been synthesized by reacting 4,4'-bipyridinium-based ligands with PdII and PtII complexes. Strict thermodynamic self-assembly of 1 and [M(en)(NO3)2] (M=Pd, Pt) 6 a,b afforded metallocycles 7 a,b. However, the synthesis of 8 a,b and 9 a,b required a self-assembly process that used sodium p-phenylenediacetate (12) as a template. Finally, metallocycles 10 a,b were synthesized under high dilution conditions from ligand 4. The formation of inclusion complexes between metallocycles 7-10 and substrates 13 and 14 were studied by low-temperature 1H NMR, and the association constants were determined in nitromethane and water by following the characteristic charge-transfer band that these metallomacrocycles show in their UV-visible absorption spectra. A clear correlation between the affinity for a substrate and the dimensions of the metallocycle was observed. Metallocycles 8 b and 9 b exhibited the highest binding constants in water and nitromethane. This observation is in agreement with the DFT (B3LYP)-optimized geometries obtained for the different metallomacrocycles, which indicate that only macrocycles 8 and 9 possess a cavity with a width larger than 3.5 A. The insertion of hydroquinone or diol 13 into the cavity of metallocycle 11 a was confirmed by single-crystal X-ray crystallography.