Octa calix arene

Bocchi et al. [5] pointed out that while the tetraacetate of p-/ T/-butyl calix[4]arene fails to form complexes with guanidium ions or Cs, the octa-(3,6-dioxaheptyl)-ether of p-/cr/-butyl calix[8]arene forms strong complexes with these cations. The Parma group [6] later showed that the hexa-(3-oxabutyl)ether of p-tert-hu y calix[6]arene also forms complexes with these ions. 

Fig. 3. HNMR (300 MHz) spectrum of tert-Cl end-capped octa-arm star M =3.76X lO g/mol) containing a calix[8]arene core...

The synthesis and characterization of novel octa-arm star blocks ((PpClSt-h-PlB)g-C8) comprising of PpClSt-h-PIB arms radiating from a calix[8]arene core are reviewed. 

FIGURE 31.5 Calixarenes used in the BLM experiments for U(IV) transport studies. I (5,ll,17,23-tetra-fert-butyl-25,26,27,28-tetra hydroxy calix[4]arene) II (5,ll,17,23,29,35-hexa-fert-hutyl-37,38,39,40,4I,42-hexa hydroxy calix[6]arene) III (5,11,17,23,29,35,41,47-octa-terr-butyl-49,50,51,52,53,54,55,56-octa hydroxy calix[8]arene) and LV (5,II,I7,23,29,35-hexa-fert-butyI-37,39,4I-tri methoxy calix [6]arene -38,40,42-triol). (Reproduced from Ramakumar, J., Nayak, S.K., and Maiti, B., J. Membr. Sci., 196, 203, 2002.)... 

Still another calixarene derivative of interest and utility is the trimethylsilyl ether. The hexa-trimethylsilyl ealix[6]arenes and octa-trimethylsilyl calix[8]arenes can be prepared 23) by using standard trimethylsilylating agents such as hexamethyldisilazene and chlorotrimethylsilane. The tetra-trimethylsilyl ethers of the calix[4]arenes, however, do not form under these conditions and require the use of the very reactive N,0-i (trimethylsilyl (acetamide 109). 

Exhaustive O-acylation was less frequently studied. The octaphosphate (Y = PO(OEt)2) , the octamesylate (Y = S02Me ), the octaesters with Y = C(0)CH = CHC6H3(OMe)2-2,4 or Y = CfOfCHBrCHs may be taken as recent examples for calix[8]arenes ° . The synthetic conditions described there may be used also in similar cases and with other calixarenes. The octa a-bromopropionates have been used as initiators for the synthesis of star polymers (atomic transfer polymerization), and the hydrolysis of the ester links was used to analyse the branches . 

Bai and co-workes reported a series of STM studies on various types of calixarenes on graphite and Au(lll) surfaces. Initially, they included p-tert-butylcalix[8]-arene in between domains of octa-alkoxyl-substituted phthalocyanine (PcOCg) monolayers on graphite [152]. The adsorption" of calix[4]arene (lower rim OH) on (111) facets of Au-beads lead to an "edge-on geometry of calixarene dimers with the lower rim pointing towards lower rim (Fig. 10.26a) [153]. 

Due to the increased number of OH functionalities, 29 pyridino homologues of p-tert-butylcalix[8]arene 21 can exist one mono-, hepta-, and octa-substituted derivatives, four di-, five tri-, eight tetra-, five penta- and four hexasubstituted regioisomers. The products of the peutial alkylation of 21 with PicCl-HCl are hitherto unknown, while fully alkylated octakis[(2-pyridylmethyl)oxy]calix[8]arene 22 has been obtained in 24% yield by using conditions similar to those described for calix[6]arene 20. From solvent extraction data, Shinkai has shown that compounds 20 and 22 display a high affinity for UO " at elevated temperature (100°C, o-dichlorobenzene) [26]. 

Kennedy s group also extended its work on the synthesis of octa-arm star block copolymers [40]. The synthetic strategy is very similar to the method described above for the synthesis of allyl group-terminated octa-arm star PIB. The synthesis involved the use of an octafimctional calix(8)arene-based initiator to initiate the polymerization of isobutylene to desirable molecular weights then st)n ene or / -chlorostyrene was polymerized to obtain the sought stars,... 

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