Influence of the chain length and metal : ligand ratio on the self-organization processes of Cu2+ complexes of [1 + 1] 1H-pyrazole azamacrocycles

Three new [1 + 1] macrocycles formed by the reaction of 1H-3,5-bis(chloromethyl)pyrazole with the tosylated amines 1,4,7,10-tetraazadecane (L1), 1,4,8,11-tetraazaundecane (L2) and 1,5,10,14-tetraazatetradecane (L3) are described. Potentiometric studies and HR-ESI-Mass spectrometry show the formation of dimeric binuclear Cu²⁺ complexes whose organization depends on the type of hydrocarbon chains connecting the amine groups. Furthermore, trinuclear or/and tetranuclear complexes are formed depending also on the length of the polyaminic bridge and on the sequence of the hydrocarbon chains. The crystal structures of the [2 + 2] [Cu₂(H(H_-1L2))₂](ClO₄)₄·4H₂O (1) and [Cu₂(H_-1L2)₂](ClO₄)₂ (2) complexes show in both of them two macrocycles self-assembled by the metal ions which interconnect their pyrazolate fragments that behave as bis(monodentate) ligands. While in 1 one central amine of each macrocycle binds to the axial position of a distorted square-pyramid and the other ones remain protonated, in 2 all the amine groups are involved in the coordination giving rise to a strongly distorted octahedral geometry. Paramagnetic ¹H NMR measurements support that these structures also form in solution. Interestingly, tetranuclear complexes [Cu₄(H_-1L4)₂(OH)_2.08](ClO₄)_2.92Br_0.54Cl_0.46 (3) and [Pd_2.39Cu_1.61(H_-1L4)₂(OH)₂](ClO₄)₂Cl_1.33Br_0.67·2.87H₂O (4) have been isolated for the macrocycle containing the 1,5,9,13-tetraamine chain (L4). 3 has two binucleating units, one of them formed by the pyrazolate moieties and their neighbouring secondary amines and the other by the two central amines of both macrocycles. This latter Cu²⁺ coordination site is completed by two hydroxide anions as bridging ligands. 4 was obtained from a solution prepared to achieve full formation of the dimeric cage [Cu₂(H_-1(HL4))₂]⁴⁺ by addition of K₂PdCl₄. The Pd²⁺ ion due to its softer acidic characteristics displaces the Cu²⁺ ions from the pyrazolate site. UV-vis spectroscopy suggests that the exchange is completed at room temperature after one hour.

Highly Selective Anion Template Effect in the Synthesis of Constrained Pseudopeptidic Macrocyclic Cyclophanes

Herein, we report the synthesis of a novel family of constrained pseudopeptidic macrocyclic compounds containing the hexahydropyrrolo[3,4-f]isoindolocyclophane scaffold and involving four coupled substitution reactions in the macrocyclization process. Although the increase in the number of steps involved in the macrocyclization could lead to a larger number of possible side products, the optimization of the methodology and the study of the driving forces have made it possible to obtain the desired macrocycles in excellent yields. A thorough computational study has been carried out to understand the macrocyclization process, and the results obtained nicely agree with experimental data. Moreover, the bromide anion had a clear catalytic template effect in the macrocyclization reaction, and surprisingly, the chloride anion had a negative template effect in opposition to the results obtained for analogous macrocycles. The parameters responsible for the specific kinetic template effect observed have been studied in detail.

The role of the side chain in the conformational and self-assembly patterns of C2-symmetric Val and Phe pseudopeptidic derivatives

Side chain as the main conformational and self-assembly structural factor for C₂-pseudopeptides.

Supramolecularly assisted synthesis of chiral tripodal imidazolium compounds

Supramolecular interactions based on amide groups direct the preferential formation of tritopic instead of monotopic or ditopic imidazolium compounds.

Polyaza metacyclophanes as ditopic anion receptors

Five macrocyclic polyaza metacyclophanes L1-L5 prepared by dipode coupling of the tosylated precursors have been studied. The basicity of the ligands has been measured potentiometrically and their ability to complex halides and perchlorate has been studied in the solid state by X-ray crystallography. The results reveal that the ligands generally act as ditopic halide receptors with even the largest, L5, being too small to envelop the anion. The ligand's basicity behaviour parallels that observed for related para-analogues. Despite the ready crystallisation of fluoride, HF2-, chloride, bromide, iodide and triiodide salts in the solid state, there appears to be little affinity for halides in aqueous solution in the pH range accessible via potentiometry. The results do give a detailed insight into the role of the aryl ring in restricting the conformational flexibility of the ligands and, hence, the ability to chelate perching anions.

Studies on the interaction of phosphate anions with N-functionalised polyaza[n]paracyclophanes: the role of N-methylation

The synthesis and interaction of N,N',N'',N'''-tetramethyl-2,6,9,13-tetraaza[14]paracyclophanes (B323Me(4)) with nucleotides and inorganic phosphates is described. An easy methodology is used to define thermodynamic selectivity. The interaction of B323Me4 and ATP has been monitored by (1)H, (31)P NMR and by molecular mechanics, ruling out the possibility of the participation of pi-stacking interactions. Results show that N-methylation is accompanied by a strong increase in the interaction of the resulting macrocycle with ATP.

Thermodynamic and Steady-State Fluorescence Emission Studies on Metal Complexes of Receptors Containing Benzene Subunits

The thermodynamic properties of the Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Pb(2+) complexes of a family of N,N'-dibenzylated open-chain polyamines are described. For comparison, similar studies are reported for polyazacyclophane macrocyclic receptors containing an aromatic subunit linking the ends of a polyamine bridge. The metal complexes of the dibenzylated ligands show lower stability constants than those reported for related nonbenzylated open-chain polyamines. On the other hand, the stability constants of these complexes are clearly higher than those found for complexes of polyazacyclophane macrocycles containing a single para-substituted benzene spacer interrupting saturated polyamine bridges. All the studied complexes follow the Irving-Williams stability order. The crystal structure of [Cu(L7)(H(2)O)](ClO(4))(2)( )()(L7 = 1-benzyl-1,5,8,12-tetrazadodecane) shows a very strongly axially distorted square planar coordination geometry for Cu(2+). Crystals of [Cu(L7)(H(2)O)](ClO(4))(2)()()(C(15)H(24)Cl(2)CuN(4)O(9)) are orthorhombic, space group P2(1)2(1)2(1), with a = 7.586(1) Å, b = 10.715(3) Å, and c = 28.13(2) Å, Z = 4, R(1) = 0.0572, and wR(2) = 0.1570. Steady-state fluorescence emission studies performed on the Cu(2+) and Zn(2+) complexes show that, while none of the Cu(2+) complexes is emissive (CHEQ effect), fluorescence emission is observed for those Zn(2+) complexes with all the nitrogen donors either protonated or coordinated to the metal ions (CHEF effect). The composition of the frontier molecular orbitals of the free-ligands and of the Cu(2+) and Zn(2+) complexes supports this behavior. The use of these water-soluble ligands as chemosensors by means of enhancement or quenching of the fluorescence emission is also discussed.