Calix arenes, formation

The coordination chemistry of tertiary phosphine-functionalized calix[4]arenes have been described.279 Treatment of a bis(diphenylphosphino) or bis(dimethylphosphino) derivative of calix[4]arene with [PtCl2(COD)] leads to the formation of the corresponding dichloroplatinum(II) complex. The related diplatinum(II) species has also been reported with the tetrafunctionalized calix[4]arene.280 The mononuclear derivative is susceptible to oligomerization if the two free phosphine ligands are not oxidized or complexed to another metal center such as gold(I).279 The platinum(II) coordination chemistry of a mono-281 and diphosphite282 derived calix[ ]arene (n = 4 and 6, respectively) has also been described. 

Figure 15. Encapsulation complexes of NOx gases with calix[4]arenes. Formation of calixarene-NO complexes (71-73). [Adapted from (72).]...

A new area of polymer science termed nano-macromolecular chemistry [Eirich, 1993] also has relevance to future polymer blend technology and application. Langmuir-Blodget techniques allow for the formation of films of one molecule thickness. Utilizing polymerizable molecules for these films, a polymer molecule or network can yield a film with the thickness of several nanometers. Alternating layers comprised of different polymers could be prepared to yield specific optical or electrical properties. Polymerization of calix-arenes to yield molecular sieving membranes for gas separation has been discussed by Conner et al. [1993]. 

Calix[n]arenes 1-3 were used as inverse PT catalysts in the alkylation of active methylene compounds with alkyl halides in aqueous NaOH solutions,and in aldol-type eondensation and Michael addition reactions. In the aikylation of phenylacetone with octyl bromide, the IPTC procedure enhanced the alkylation versus hydrolysis and C versus O alkylation selectivities with respect to those observed xmder classical PTC reactions in the presence of tetrabutylammonium bromide (TBAB) or hexadecyltributylammonium bromide (HTPB). Moreover, the aqueous catalyst solution was easily separated from the organic phase eontaining the products, and no organic solvent was required. In the case of the aldol-type condensation of benzaldehyde with indene or acetophenone in aqueous NaOH (Fig. 9), IPTC reaetions eatalyzed by I were compared with those conducted in aqueous micelles in the presence of cetyltrimethylammonium bromide (CTAB) as the sufactant. Although selectivities and yields were similar, the IPTC proeedure avoided the formation of emulsions, thus faciUtating product separation and catalyst recovery. In the light of the results obtained, water-soluble calix[ ]arenes 1-3 were proposed... 

Another example involves the preparation of novel polymers containing W calix-arenes. Such materials, formed by the electropolymerization of species 7.51 (Scheme 7.10), show high conductivity values of up to 15.5 Scm . It was possible to use the resultant polymers to specifically recognize p-xylene. For example, formation of the polymers with R=adamantyl in the presence of p-xylene led to films with a 10-fold increase in conductivity over those formed in the absence of xylene or in the presence of toluene [92]. 

For calix[5]arenes, similarly to calix[4]arenes, formation of inclusion dimers is observed for unsubstituted at upper rim or substituted with small e.g. methyl groups calix[5]arenes. As an example para-methylated calix[5]arene is shown in Fig. 38.17a [37]. 

A set of oxygen donor atoms, providing both a and tt donation to a metal center, is not appropriate to stabilize any low oxidation state of a metal.19 This is, however, a synthetic advantage since very reactive, unstable, low-valent metalla-calix[4]arenes can be generated in situ and intercepted by an appropriate substrate. In the absence of a suitable substrate, the reactive fragment, however, can collapse to form metal-metal bonded dimers. The formation of metal-metal bonds has been, however, so far observed in the case of Group V and VI metals only. The most complete sequence so far reported has been for tungsten, molybdenum, and niobium. 

Chloroform solutions of calixarenes (33 38)293,354 show high affinity for Au111 and good selectivity over Fe111 in some cases.293 Spectroscopic data indicate that complex formation with thioethoxy calix[4]arenes involves formation of inner-sphere complexes with Au—S bonds.354... 

It had been reported that fullerene Cgo forms a water-soluble complex with y-cyclodextrin by heating with an excess amount of y-cyclodextrin in water [10] or in a mixture of refluxing water and toluene for a long time, such as 30 h [ 11]. The isolated complex is considered to have the Cgo structure bicapped with y-cyclodextrin in a molar ratio of 1 2 [11], and the complex dissolved in water to give a solution of C o with a concentration of nearly 10 mol L 410,11 ]. Fullerene Qo was also solubilized in water by complexation with a sulfocalix[8] arene, i.e., calix-[8]aryloxy-49,50,51,52,53,54,55,56-octakis(propane-3-sulfonate). The concentration of this complex in water is estimated as 5x10 mol L [12]. Complex formation between fullerene and various calixarenes has also been reported [8]. 

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