Functionalized Calixarenes

The bromination and acetylation reactions show that the calixarenes are capable of undergoing conventional electrophilic substitution reactions without rupture of the macrocyclic ring. Zinke et al.18) reported the nitration of p-tert-butylcalixarene (ring size uncertain) and obtained a material that failed to melt up to 400 °C, exploded when heated more strongly, and had a nitrogen analysis in agreement with a tetranitro-calixarene. Attempts to obtain a nitration product from calix[4]arene 59, 

As an alternative to electrophilic substitution as a means for introducing functional groups into the calixarenes, a reaction sequence has been developed that involves the conversion of calix[4]arene (59) to the tetraallyl ether 63. When 63 is heated in diethylaniline it undergoes a four-fold p-Claisen rearrangement to afford p-allyl-calix[4]arene (62) in excellent yield 126). From the tetra-tosyl ester of 62 (i.e. compound 66 a) a variety of functionalized calixarenes have been obtained, including the aldehyde 66b, alcohol 56 c, bromide 66 d, azide 66 e, amine 66f, and nitrile 66g. Removal of the tosyl group occurs under mildly basic conditions to yield, for example, p-(2-hydroxyethyl)calix[4]arene (66 h). 

The cavitand 53 (R = Br) provides another precursor for the preparation of a functionalized ealixarene. Bromination of the octahydroxycalixarene 13 prior to the 

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Progress in molecular recognition of functionalized calixarenes with hetero-atomic bridges as synthetic receptors 99MI43. 

Dozol, J.F., Dozol, M., Macias, R.M. 2000. Extraction of strontium and cesium by dicarbollides, crown ethers and functionalized calixarenes. J. Incl. Phenom. Macrocycl. Chem. 38 (1-4) 1-22. 

Dozol, J.F., Bohmer, V., McKervey, A. et al. 1997. New macrocyclic extractants for radioactive waste treatment Ionizable crown ethers and functionalized calixarenes. Report EUR-17615. 

Bis-Diglycolamides [252] CMPO-functionalized calixarenes [253,254] CMP(0)-functionalized C-pivot tripodes 257—259]... 

These compounds, tested in NPHE at Cadarache, were used as reference compounds for the extraction of actinides by functionalized calixarenes (see below). The distribution ratios for neptunium mainly at the oxidation state (V), plutonium at the oxidation state (IV), and americium (III) are shown in Table 4.21 for OOCMPO. They were also used as references for the americium over europium selectivity (Table 4.22). 

J.-F. Dozol, V. Bohmer, M. A. McKervey, F. Lopez-Calahorra, D. N. Reinhoudt, M. J. Schwing, R. Ungaro and G. Wipff, New macrocyclic extractants for radioactive waste treatment Ionizable crown ethers and functionalized calixarenes, EUR-OP Reference CG-NA-17615-EN-C (EUR-17615), European Commission, Nuclear Science and Technology, Luxembourg, 1997. 

L. H. Delmau, Ph.D. Thesis, Strasbourg University, 1997. Extraction of Trivalent Lanthanides and Actinides by Functionalized Calixarenes. Study of the Structure of the Complexes in Solution by Nuclear Magnetic Resonance. 

Grander, M., Dozol, J.F., Asfari, Z., Vicens, J. 1999. Simultaneous removal of technetium and cesium by functionalized calixarenes from acidic liquid waste. J. Radioanal. Nucl. Chem. 241(1) 59-67. 

Another strategy for functionalizing calixarenes is to strap the macrocydes. Several systems bearing a diamido strap have been prepared and have shown a selectivity for acetate anions (e.g., receptor 10 Ka=103M 1 in CDC13) [49]. Similar selectivity preferences were observed for thiacalix[4]arene receptors functionalized with four ureido or thioureido units on the lower rim [50]. 

We have reported the synthesis of functionalized calixarene 60. The crystal structure of the nickel azide complex of this dinuclear host indicates two nickel ions bound (one centered in each of the appended lower rim macrocycles), with three unique azide 1,1 end on bridging ligands cascaded in between (Fig. 6) (152). 

Figure 5. Schematic representation of different classes of Eu3 + and Tb3 + complexes with encapsulating ligands (a) cryptates (b and c) complexes of branched macrocyclic ligands (d) podates and (e) complexes of functionalized calixarenes.

Encapsulation of the Eu3 + and Tb3 + ions by cage-like ligands was also achieved using functionalized calixarenes. Metal luminescence properties were studied mostly for complexes of calix[4]arenes, while few results are available for complexes of calix[6]arenes and calix[8]arenes, with the latter being dinuclear complexes. Figure 13 schematically shows the calixarene ligands of the Eu3+ and Tb3+ complexes examined. Some photophysical data and the number of coordinated solvent molecules of these complexes are gathered in Table 4. 

CEA Cadarache and seven European universities were involved in a research programme to synthesize and test new macrocyclic extractants (crown-ethers and calixarenes). The main aim of this study was to selectively remove caesium, strontium and actinides from medium level liquid waste (MLLW) to decontaminate them to the extent that they can be disposed of in a near surface site. A new calixarene has been synthesized by the University of Parma, which has a cesium/sodium selectivity 100 times higher than that of the best current extractant for cesium. The large selectivity of this molecule has been explained theoretically. The results obtained for cesium extraction from simulated MLLW have been confirmed with real HLLW. Finally, new functionalized calixarenes have been also synthesized, which are more selective to actinides and lanthanides than the best extractant available on the market. 

Crown ether-functionalized calixarene 2.168 (Chart 1.36) in which two bithiophene units were attached at the termini of a calixarene moiety was prepared by a similar procedure to that described above for 2.167... 

Sannicolb et al. synthesized cyclopentadithiophene (CPDT)-functionalized calixarene moieties 2.170 and... 

Functional calixarenes can be used as plurifunctional ATRP initiators for the synthesis of star polymers. Show the structures of 2-bromopropionate and 2-bromoisobutyrate esters of 4-ten-butyl calix[ ] arene used as tetrafunctional ( = 4), hexafunctional (h = 6), and octafunctional (n = 8) initiators for ATRP. 

Transfer of selectivity from the lower to the upper rim is the most useful method for the selective synthesis of partially functionalized calixarenes at the upper rim. Indeed, one can exploit the different reactivity of aryl ethers compared to phenols to introduce, regioselectively, additional functional groups at the upper rim of partially alkylated calixarenes. Moreover, if l,3-dialkoxy-/ -r rt-butylcalix[4]arenes are submitted to the reverse Friedel-Crafts reaction, the tert-hwiyX groups are detached only from the para position of the phenolic nuclei, obtaining compounds where only two diametral aromatic rings are available for further functionalization. 

Figure 13 illustrates all the known modes of cation binding by native and functionalized calixarenes exploiting cation-TT, induced dipole, or electrostatic interactions. Strictly speaking, only for situations (c)-(f), we can talk of cation recognition by calixarene receptors, whereas in metallation with transition and f-element (situations (a) and (b)), which are often exploited in anion complexation or catalysis, little control is experienced on selectivity. Usually, the most important calixarene-based cation receptors are obtained by the introduction of chelating units at the lower rather than at the upper rim. This ensures a more... 

R. Ungaro, A. Arduini, A. Casnati, et al., Complexation of ions and neutral molecules by functionalized calixarenes, in Computational Approaches in Supramolecular Chemistry, ed. G. Wipff, Kluwer Academic Publishers, Dordrecht, 1994, pp. 277-300. 

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