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1,3-Alternate calix[4]arenes were prepared, having bulky adamantyl groups in the p-positions of all four aromatic units of the macrocycles and pairs of propargyl or 2-azidoethyl groups alternating with n-propyl groups at the phenol oxygen atoms. The step-wise syntheses were carried out through a selective distal alkylation of the parent p-adamantylcalix[4]arene with propargyl bromide or 1,2-dibromoethane, resulting in calix[4]arenes bearing pairs of propargyl or 2-bromoethyl groups at their narrow rims. The bromine atoms were replaced by azide groups, and then both calix[4]arene diethers were exhaustively alkylated at the remaining OH-groups with 1-iodopropane under stereoselective conditions to fix the macrocycles in an 1,3-alternate shape. The structures of the prepared p-adamantylcalix[4]arenes were confirmed by NMR and HRMS data, and, for the 1,3-alternate dipropargyl ether, the X-ray diffraction data were also collected. Preliminary data on the reactivity of the prepared calixarenes under the CuAAC conditions suggested a strong steric hampering created by the adamantane units nearby the reacting alkyne or azide groups that affected the outcome of the two-fold cycloaddition involving the calixarene bis(azides) or bis(alkynes) as complementary partners. [ABSTRACT FROM AUTHOR]

Copper(I)-catalyzed azide-alkyne cycloaddition was employed to construct biscalixarene assemblies from the calix[4]arene dipropargyl ethers and 4,4′-bis-azidomethylated azobenzene or stilbene. Three bis(calixarenes) having the calix[4]arene cores linked to each other by pairs of (E)-azobenzene/stilbene units through four triazole groups were obtained as confirmed by NMR, HRMS and X-ray diffraction data. Nevertheless, the formation of larger macrocycles and polymeric/oligomeric products was found to be the major competing process that seriously limited the applicability of the one-step macrocyclization approach for the construction of photoresponsive biscalixarene assemblies linked by pairs of azobenzene/stilbene units. [ABSTRACT FROM AUTHOR]

Cone calix[4]arenes and calix[6]arenes bearing two, three, and four short peptide units each having two chiral carbon atoms were prepared. The syntheses were performed by using an efficient modular approach that includes the Ugi preparation of the azido-peptide followed by its reactions with the propargylated calixarenes under CuAAC (CuI-catalyzed azide-alkyne cycloaddition) conditions. The three novel multitopic hosts were probed for their ability to bind metal ions by UV titration, and showed the highest complexation efficiency towards copper(II) and lead(II). These two cations possessed quite different complexation modes with copper(II) bound predominantly by multiple-triazole sites, in contrast to lead(II), which is stabilized mainly by multiple interactions with amide groups of the peptide units. Circular dichroism data for the free chiral hosts, their equimolar mixtures with copper(II) perchlorate and lead(II) perchlorate, and for tertiary mixtures of all three compounds showed the formation of mono- and binuclear complexes, or a switching behavior, depending on the structure of the host and the addition order of the cations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Calix[4]arenes with 1,2,3-triazole and 1,3-diketone groups as ligands of Eu3+ (La)3+. • Diversity in complex stoichiometry from UV–Vis and NMR data in solutions. • NMR data under slowed down ligand exchange regime specify binding sites of Eu3+ (La)3+. • DFT data reveal complex structures in correlation with their thermodynamic parameters. • Optimal complex structure for greatest Eu3+- luminescence is demonstrated. The present work introduces two calix[4]arenes (cone and 1,3-alternate isomers) bearing pairs of 1,2,3-triazole and 1,3-diketone groups as binding sites of Eu3+ (La3+) ions. Combination of UV–Vis, 1H NMR spectroscopy and DFT calculations allowed to evaluate the structure of the lanthanide complexes and specify the groups participating in the coordination. It was found that cone calix[4]arene forms the 2:1 (ligand: Ln3+) complex arisen from the coordination of Ln3+ ions via both 1,2,3-triazole and 1,3-diketonate groups as well as the 2:2 complex form, where Ln3+ ions are coordinated via 1,3-diketonate groups only. The quantum chemical calculations reveal that the 2:2 complex is more thermodynamically favorable than the 2:1 one, which correlates with the NMR data. It is worth considering the coordination of Ln3+ ions with both triazole and 1,3-diketonate groups as the reason for the specific slowed down ligand exchange for 2:1 and 2:2 complex forms. The comparative analysis of the Eu3+-centered luminescence reveals the cone calix[4]arene as more efficient antenna for Eu3+ ions than the 1,3-alternate calix[4]arene, where 1,2,3-triazole and 1,3-diketone substituents are localized at the opposite sides of the macrocycle. The growing degree of accumulation of the 2:1 complex is followed by an increase in Eu3+-centered luminescence for both calix[4]arene ligands. [ABSTRACT FROM AUTHOR]