Major calixarenes

Especially well elaborated procedures exist for the three major calixarenes 2a, 2c and 2e ... 

The original Zinke synthesis employed NaOH as the base to induce the condensation of / -alkylphenols and formaldehyde, and base induction remains the method of choice noi only for the three major calixarenes 2, 4, and 6 (R = tert Bu) but also for the two minor calixarenes 3 and 5 (R = tert B x). With NaOH (in small amounts) as the base and refluxing diphenyl ether as the solvent, a 50% yield of pure p-rcrr-butyicalix[4]arene 2 is produced."" With KOH (in larger amounts) as the base and refluxing xylene as the solvent, ca. 85% yields of p-tert-butylcalix[6]arene 4 are produced.With NaOH (in small amounts) as the base and refluxing xylene as the solvent, ca. 65% yields o/p- err-butylcalix[8]arene d are produced.The p- crr-butylcalix[5]arene and p-... 

The majority of the literature reports deal with the reaction of calixarenes with Group I and II cations. Polymeric calixarenes have been the subject of a more recent innovation. Harris et al. [23] have prepared a calix[4]ar-ene methacrylate, its polymerization, and Na complex-ation (Scheme 3). They concluded that both monomers and polymers form stable complexes with sodium thiocyanate. 

Metalated container molecules can be viewed as a class of compounds that have one or more active metal coordination sites anchored within or next to a molecular cavity (Fig. 2). A range of host systems is capable of forming such structures. The majority of these compounds represent macrocyclic molecules and steri-cally demanding tripod ligands, as for instance calixarenes (42), cyclodextrins (43,44), and trispyrazolylborates (45-48), respectively. In the following, selected types of metalated container molecules and their properties are briefly discussed and where appropriate the foundation papers from relevant earlier work are included. Porphyrin-based hosts and coordination cages with encapsulated metal complexes have been reviewed previously (49-53) and, therefore, only the most recent examples will be described. Thereafter, our work in this field is reported. 

He also prepared a poly(styrene-g-styrene) polymer by this technique [114], The lack of crosslinking in these systems is indeed proof of the control achieved with this technique. An eight-arm star polystyrene has also been prepared starting from a calixarene derivative under ATRP conditions [115]. On the other hand, Sawamoto and his coworkers used multifunctional chloroacetate initiator sites and mediation with Ru2+ complexes for the living free-radical polymerization of star poly(methylmethacrylate) [116,117]. More recent work by Hedrick et al. [84] has demonstrated major progress in the use of dendritic initiators [98] in combination with ATRP and other methodologies to produce a variety of structure controlled, starlike poly(methylmethacrylate). 

Based on the theory, the separation of enantiomers requires a chiral additive to the CE separation buffer, while diastereomers can also be separated without the chiral selector. The majority of chiral CE separations are based on simple or chemically modified cyclodextrins. However, also other additives such as chiral crown ethers, linear oligo- and polysaccharides, macrocyclic antibiotics, chiral calixarenes, chiral ion-pairing agents, and chiral surfactants can be used. Eew non-chiral separation examples for the separation of diastereomers can be found. 

Following the recommendation of Reinhoudt,23 in almost the majority of cases, nitrophenyl alkyl ethers were used as diluents for the extraction tests by the Cadarache group, because they are able to dissolve calixarenes at relatively high concentration. Moreover, the basicity as well the dielectric constant of these diluents improves cation extraction by better solvation of the associated nitrate anions (Table 4.3). 

Electrospray Ionization/Mass Spectrometry (ES/MS), a soft-ionization desorption technique using polar solvents such as water, methanol, or acetonitrile, was used for direct measurement of cations in solution. The first measurements carried out with mono or bis(crown-6) calix[4]arenes from an equimolar cation-extractant solution confirm that the calixarenes mono(crown-6) extract only one cesium cation. On the contrary, in the same conditions, bis(crown-6) calix[4]arenes can extract two cesium cations for a ratio Cs/BC6 equal to 2.5. The binuclear complex (composed of two cesium cations) is the major species. Cesium/sodium selectivity measurements implementing various mono or bis(crown-6) calix[4]arenes were in agreement with liquid/liquid results.42... 

This difference of behavior of calixarenes bearing CMPO residues either on the wide rim or on the narrow rim was confirmed by extraction of europium (from nitric acid solutions by CPw2 and CPn2 diluted in chloroform) by implementing ESI-MS for the two calixarenes. Complexes with 1 1 and 1 2 Eu calix-CMPO stoichiometry were evidenced. The major species for CPw2 is the 1 2 complex, while for CPn2 the predominant complex is the 1 1 complex.165... 

The majority of the devices mentioned thus far rely on the Hofmeister series for anion selectivity. However, for anions that deviate from this series, organometallic receptors can be utilised. The type of ligand or metal centre will influence the sensor selectivity due to the characteristics of the electron acceptance of the complex. An interesting development that is being explored here is the use of calixarenes. These have previously found use as cation-selective species, but with suitable substitution are now being incorporated within anion-selective devices. Compounds suitable as receptors for halides [61],benzoate [61] and acetate [62] have been developed. Reinhoudt and his co-workers have reported the production of a POj-selective CHEMFET based on a uranyl cation immobilised within a salophene ligand (Fig. 5), which shows selectivity over more lipophilic anions such as Br" and NOj [63]. 

This subject was covered previously in pages 993-1022 in CHEC-II(1996) (volume 9, chapter 36). This chapter is intended to update the previous work on major preparative and structural aspects of various types of rings containing silicon to lead that have been reported since 1995. As compared to previous work, two novel topics are covered reactivity and transformations of heterocyclic rings in Section 14.19.4 and application of computational methods in Section 14.19.5. Moreover, silacrown ethers and related compounds such as calixarenes, cyclophanes, and metallacenes are covered in Section 14.19.3.6. 

The facile condensation reaction between formaldehyde and phenols or their derivatives provides a major route into rigid macrocycles used in supramolecular chemistry. Calixarenes, the best-known class of phenol-derived macrocycles, are prepared this way, as are spherands and their relatives. Cyclotriveratrylene, however, is an excellent exemplar of the molecular basket type of ligand and has been known for the best part of a century. The basic cyclotriveratrylene synthesis is shown in Figure 3.1. The original procedure by Mrs. Gertrude Maud Robinson [1] has since been refined by others and many variations are known [2,3]. 

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