Search results for "calixarene"

Stepwise synthesis and selective dimerisation of bis- and trisloop tetra-urea calix[4]arenes.

2008

Tetra-urea calix[4]arenes substituted with four mono- or bisalkenyl residues have been converted into bis- or tetraloop compounds by intramolecular olefin metathesis, with use of a tetratosylurea calix[4]arene as template. The same strategy has now been used to synthesise trisloop compounds and bisloop compounds with adjacent loops, completing the series of the loop-containing tetra-urea derivatives. A tetra-urea calix[4]arene of the AABB type, where A stands for a bisalkenyl- and B for a monoalkenyl-substituted urea unit, was used as precursor for the three loops. It was easily synthesised from a tetraamino calix[4]arene in which two adjacent amino groups were Boc-protected. The ABCB-type …

ChemInform Abstract: Chirality in Calixarenes and Calixarene Assemblies

2001

The synthesis of double-calixarenes

1989

Abstract Macrocyclic molecules consisting of two calix[4]arene moieties linked via their p-positions by one 1, two 2 or four 3 aliphatic chains were synthetized for the first time.

Bis-ferrocene derivatives of bridged calix[4]arenes: syntheis, X-ray crystal structure and electrochemical properties

1991

The reaction of chlorocarbonylferrocene (2) with bridged calix[4]arene macrocyclic compounds, in which two opposite para-positions are connected by an additional aliphatic chain where n = 5 (1a) or n = 8 (1b) respectively, gave the corresponding new redox-active bis-ferrocene derivatives of bridged calix[4]arenes, 3a and 3b. An X-ray diffraction study of 3a shows that the caliz[4]arene has a cone conformation in which the two ferrocene substituents are located on the phenolic units connected to each other by the aliphatic chain bridge. Cyclic voltammetric and coulometric studies in dichloromethane reveal that 3a and 3b undergo reversible two electron oxidations at + 0.90 V (versus SCE), sug…

Compensation of steric demand by cation–π interactions, cobaltocenium cations as guests in tetraurea calix[4]arene dimers

2003

The affinities of ferrocene (2) and the cobaltocenium cation (3+), which have roughly the same size and differ in their charge, towards the inner cavity of the dimeric capsule formed by tetraurea calix[4]arene (1) were studied in C2D4Cl2 solutions. While 3+, which occupies more than 75% of the internal volume of the dimer, is readily encapsulated this is not the case for 2. This is probably due to cation-pi interactions, which operate only between 3+ and the aromatic rings of the calix[4]arene dimer. We found that the affinity of the cobaltocenium cation is higher than that of the tropylium cation (4+) and is only 2-3 times less than that of the tetraethylammoniun cation (5+). From the vari…

Noncovalent assembly of functional groups on calix[4]arene molecular boxes

1997

Calix[4]arenes diametrically substituted at the upper rim with two melamine units spontaneously form well-defined box-like assemblies in the presence of two equivalents of 5,5-diethylbarbituric acid. These assemblies, consisting of nine different components, are held together by 36 hydrogen bonds and are stable in apolar solvents at concentrations of up to 10-4M. This paper reports the first X-ray crystal structure, and the MALDI TOF mass spectra together with the complete 1H NMR spectroscopic characterization of these hydrogen-bonded assemblies. The crystal structure clearly shows that the assemblies are stereogenic, as a result of the antiparallel orientation of the two rosette motifs. Fu…

Rational Synthesis of Multicyclic Bis[2]catenanes

2004

Bis-loop tetraurea calix[4]arene 6 has been prepared by acylation of the wide-rim calix[4]arene tetraamine 1 with the activated bis(urethane) 8 under dilution conditions. Similarly the bis(Boc-protected) tetraamine 2 is converted into the mono-loop derivative 3 which after deprotection and acylation gives the bisalkenyl derivative 5. In apolar solvents this tetraurea calix[4]arene 5 forms regioselectively a single hydrogen-bonded homodimer, from which the bis[2]catenane 10 a is formed in 49 % by a metathesis reaction followed by hydrogenation. Bis-loop derivative 6 forms no homodimers for steric reasons, but a stoichiometric mixture with the open-chain tetraalkenyl derivative 7 a contains e…

A Self-Sorting Scheme Based on Tetra-Urea Calix[4]arenes

2009

Size and shape do matter: When dimerized in nonpolar solvents, an equimolar mixture of eleven tetra-urea calix[4]arenes with different wide-rim substituents self-sorts into only six out of 35 different homo- and heterodimers (see picture). Since the calixarene scaffold and the four urea units are the same in all cases, the self-sorting process is driven only by the cooperative action of steric requirements and stoichiometry.

Strontium complexes of calixarene amides in the solid state: structural dependence on the ligand size and on the counter ions

2000

For the first time, crystal structures of three strontium complexes of calixarene amides have been determined. A p-tert-butylcalix[6]arene hexaamide forms a 1∶1 complex with Sr(Pic)2 (Pic = picrate), whereas p-tert-butylcalix[8]arene and p-methoxycalix[8]arene octaamides encapsulate two strontium cations each. The binding geometries of the metal cations depend on the ligand size and on the counter anion used (chloride or picrate).

Dimeric Capsules Formed by Tetra-CMPO Derivatives of (Thia)Calix[4]arenes

2010

Thiacalix[4]arene 2, calix[4]arene 3 a and its tetraether fixed in the cone conformation 3 b form homo- and heterodimeric capsules in apolar solvents, which are held together by a seam of NH⋅⋅⋅O=P hydrogen bonds between carbamoylmethyl phospine oxide functions attached to their wide rim. Their internal volume of ∼370 A3 requires the inclusion of a suitable guest. Although neutral molecules such as adamantane (derivatives) or tetraethylammonium cations form kinetically stable complexes (1H- and 31P-time scale), the included solvent is rapidly exchanged. The internal mobility of the included tetraethylammonium cation is distinctly higher (ΔG=42.5 and 49.7 kJ mol−1 for 3 a and 3 b) than that f…