Arturo Arduini

The preparation and properties of a new lipophilic sodium selective ether ester ligand derived from p-t-butylcalix[4]arene

Abstract A new lipophilic cation ligand (2), which shows selectivity for sodium in extraction experiments, has been obtained by the reaction of p-t-butylcalix[4]arene and t-butyl bromoacetate. The X-ray crystal structure determination and 1H and 13C NMR studies show compound (2) in a fixed “cone” structure both in the solid state and in solution. Compound (2) in apolar media strongly encapsulates sodium cation with a 1:1 stoichiometry and is able to separate the tight sodium picrate ion pair in THF.

p-t-Butylcalix[4]arene tetra-acetamide: a new strong receptor for alkali cations [1]

From the reaction ofp-t-butylcalix[4]arene with α-chloro-N,N-diethyl acetamide a new lipophilic ether-amide ligand (2) has been obtained in high yield. Solution studies show (2) to be a very strong cation receptor for alkali cations, especially sodium and potassium. The X-ray crystal structure determination of the free ligand (2) and two potassium complexes (KI and KSCN) shows the calix[4]arene in a fixed ‘cone’ structure and the cation completely encapsulated in a polar cavity of eight oxygen atoms.

Chloromethylation of calixarenes and synthesis of new water soluble macrocyclic hosts

Abstract The chloromethylation of calix[4]arene 1a and of the methyl ethers of calix[6]arene 1b and calix[8]arene 1c , using chloromethyl n-octyl ether and SnCl 4 in chloroform at room temperature has been performed in good yield for the first time. The chloromethylated products 2a–c have been used as intermediates to introduce on calixarenes phosphonic acid groups which render these macrocycles water soluble and potentially useful in Host Guest Chemistry.

Rigidified Calixarenes Bearing Four Carbamoylmethylphosphineoxide or Carbamoylmethylphosphoryl Functions at the Wide Rim

Conformationally rigidified tetraCMPO derivatives have been prepared from calix[4]arene bis(crown ether) 4a in which adjacent oxygens are bridged at the narrow rim by two diethylene glycol links. Acylation of the tetraamine 4c with the CMPO-active ester 5b gave the tetraphosphine oxide 6a, while the tetraphosphinate 6b and the tetraphosphonate 6c were obtained by Arbuzov reaction of tetrabromoacetamido derivative 7 with PhP(OEt)2 or P(OEt)3. The extraction ability of these CMPO derivatives was checked for selected lanthanides and actinides and compared with the analogous compounds 1b, 10b and 10d derived from calix[4]arene tetrapentyl ether. All rigidified bis(crown ether) ligands are more effective extractants than their pentyl ether counterparts and require only 1/10 of the concentration (cL= 10 4M) to obtain the same distribution coefficients, while with CMPO itself a 2,000-fold concentration is necessary. This could be a consequence of a better preorganisation of the ligating functions owing to the rigidity which on the other hand did not change the observed selectivity for americium (DAm/DEu=9-19) and for light lanthanides over heavy ones. NMR relaxivity titration curves show that the complex of Gd3+ with ligand 6a is highly oligomerised in anhydrous acetonitrile over a large range of ligand:metal concentration ratios. Nuclear magnetic relaxation dispersion (NMRD) profiles also showed that large oligomers were formed, and their mean tumbling times were deduced from the Solomon-Bloembergen-Morgan equations. The NMR spectra of dia- and paramagnetic lanthanide complexes with 6a agreed with the presence of two conformers with an elongated calix[4]arene skeleton in which the distances between opposite methylene groups are different. Contrary to what was observed with ligand 2a, the addition of nitrate ions does not labilize the metal complexes, presumably because of the rigidification effect of the ether bridges. Single-crystal X-ray structures were obtained for the active ester 5b and for diphenylphosphorylacetic acid 5a.

Toward Directionally Controlled Molecular Motions and Kinetic Intra- and Intermolecular Self-Sorting: Threading Processes of Nonsymmetric Wheel and Axle Components

We have investigated the self-assembly of pseudorotaxanes composed of viologen-type axle and calix[6]arene wheel components. The distinctive feature of this system is that both components are structurally nonsymmetric; hence, their self-assembly can follow four distinct pathways and eventually give rise to two different orientational pseudorotaxane isomers. We found that the alkyl side chains of the viologen recognition site on the molecular axle act as strict kinetic control elements in the self-assembly, thereby dictating which side of the axle pierces the calixarene cavity. Specifically, nonsymmetric axles with alkyl side chains of different length thread the wheel with the shorter chain. Such a selectivity, in combination with the face-selective threading of viologen-type axles afforded by tris(N-phenylureido)calix[6]arenes, enables a strict directional control of the self-assembly process for both the face of the wheel and the side of the axle. This kinetic selectivity allows both intramolecular self-sorting between two different side chains in a nonsymmetric axle and intermolecolar self-sorting among symmetric axles with alkyl substituents of different length.

Rigid cone calix[4]arenes as π-donor systems: complexation of organic molecules and ammonium ions in organic media

One step synthesis of calix[4]arene biscrowns, with a rigid cone structure and alkyl or phenyl groups at the ‘upper rim’, has been performed. The binding ability of these rigidified cone calix[4]arenes 1–4,13 has been evaluated, in apolar organic media, towards neutral organic molecules and ammonium cation salts. Comparison with more flexible analogues 5,6,11 shows that only rigid cone calix[4]arenes are able to complex organic species. The association constants strongly depend on the type of substituents present at the upper rim. The X-ray crystal structure of the endo complex p-cyclohexyl-25,26-27,28-biscrown-3-calix[4]arene 3 with CH3NO2 has been resolved.

A general synthesis of calix[4]arene monoalkyl ethers

Abstract A method for the first general and high yield synthesis of calix[4]arene monoalkyl ethers (4) has been developed by treating the easily available tetra -(2) or dialkyl ethers (3) with the equivalent amount of iodotrymethylsilane in CHCl3.

Selective functionalization of calix[4]arenes at the upper rim

Methods are described for the selective diametrical functionalization of calix[4]arenes at the upper rim by transfer of functionality and selective substitutions at the para positions of the phenol rings. The crystal structure of 26,28-dimethoxy-11,23-dinitrocalix[4]arene is described.

Solid State Studies on p.t-Butyl-Calix[6]Arene Derivatives

Calix[n]arenes1 (1) are a class of phenol-formaldehyde macrocyclic oligomers which exhibit different sizes and shapes depending on the number of phenolic units in the cyclic array and on the nature of substituents on the aromatic nucleus (R1) and on the phenolic oxygen (R2).

Synthesis of 1,2-bridged calix[4]arene-biscrowns in the 1,2-alternate conformation

New methods to obtain 1,2-bridged calix[4]arene-biscrowns in the 1,2-alternate conformation are described. The stereochemistry of the proximal double functionalization reaction is mainly governed by the solvent, the length of the polyether units and the base used to deprotonate the calix[4]arene.