Calix arenes functions

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. 

Reinhoudt at al. have recently reported [48] the preparation of a calix[4]arene functionalized with two Zn(II) centers 25, which is highly efficient on transesterification of HPNP. The dimer complex is reported to be 50 times more active (in 50 (v/v)% acetonitrile-water at pH = 7.4 and I = 298 K) than the corresponding monomer (26) which is itself 6 times more active than 27, implying the contribution of the calix[4]arene moiety in the mechanism. The saturation kinetic experiments showed high association constant for the catalyst-substrate complex (K -... 

Figure 1.4 Calix[4,6]arene functionalized with a phosphoryl linkage for complex-ation of radionuclides.

The introduction of nitro groups at the upper rim of calix[4]arenes is a quick and useful method for the preparation of functionalized calix[4]arenes. This reaction is quite general and can be conveniently carried out on a wide variety of calix[4]arenes substituted at the lower rim. When the starting calix-arene is partially substituted at the lower rim, the substitution takes place at the more reactive phenol rings. 

Four examples are known of calix[6]arene derivatives which have been used as receptor molecules in potentiometric measuring devices. Calix[6]arene 36 functionalized with six ethylester moieties showed a moderate selectivity for hexylammo-nium ions in the presence of smaller primary alkylammonium ions (logA = —1.0 to — 1.4) in ion-selective electrodes [140]. The same derivative 36 also proved to be sensitive towards Cs ions [141]. CHEMFETs with calix[6]arenes, functionalized with three diethylamido moieties (37) or with three phosphate moieties (38), are selective for guanidinium ions [142]. The fourth example is calix[6]arene 39 functionalized with two thiophosphoryl groups which is selective for Pb " ions... 

Of those functional crystalline assemblies with structures that conform to polyhedra, it is the prisms that have, thus far, been most studied. In particular, Rein-houdt has described a 3D assembly with a structure that conforms to the simplest prism namely, a trigonal prism.53 Specifically, three calix[4]arenes functionalized at the upper rim with two melamine units have been shown to assemble with six barbituric acid molecules via 36 hydrogen bonds to form a nine-component assembly with a structure that approximated a trigonal prism (Fig. 31). Although the cavity of the assembly was too small to accommodate a guest, the assembly packed to produce voids that included toluene molecules as guests. 

Upper rim calix[4]arenes functionalized with two and four ruthenium(II) bi-pyridyl amide groups (136 and 137) have very recently been prepared (258). These receptors also sense the presence of dihydrogen phosphate anions selectively. 

Calixarenes have attracted the attention of a number of groups for constructing a wide variety of receptors. Functionalized higher calix[ ]arenes ( = 6 and 8) are also being increasingly synthesized. 

S. Rizzo, F. Sannicolo, T. Benincori, G. Schiavon, S. Zecchin and G. Zotti, Calix[4]arene-functionalized poly-cyclopenta[2,l-fc 3,4-fc ]bithiophenes with good recognition abihty and selectivity for small organic molecules for application in QCM-based sensors, J. Mater. Chem., 14, 1804-1811 (2000). 

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. 

Stoikov et alP synthesized novel p-tert-hnty thia-calix[4]arenes functionalized with hydrazide groups at the lower rim of the cone and the partial cone in the 1,3-altemate conformations. The affinity of the self-assembly to p-(Al +, Pb +) and c -(Fe +, Co +, Ni +, Cu ", Ag" ", Cd " ") block elements was investigated by... 

Scheme 3.2 shows per-functionalized pillar[5]arene derivatives prepared from per-hydro)ylated pillar[5]arene 3.6 as a starting compound. Applying an efficient organic reaction is required for the perfect introduction of functional groups at all 10 reaction sites. A straightforward and efficient functionalization process for per-hydroxylated pillar[5]arene is etherification, which has been used for functionalization of the lower rims of phenolic moieties in calix[ ]arene derivatives. Various functionalized pillar[5]arene derivatives can be obtained by etherification of per-hydroxylated pillar[5]-arene with an alkyl-halide in the presence of appropriate bases, such as NaH and K2CO3. Introduction of the substituents can change various physical... 

A unique example of a chiral calix[4]arene functionalized at the upper rim with an amino acid is the aminophosphonic acid derivative 8 (Fig. 2.2). Its synthesis using Pudovik-type addition was reported recently by the group of Kalchenko... 

A new design was published in 2006, featuring calix[4]arenes functionalized in the 1,2-, 1,3- and 1,2,3-positions of the upper rim with [12]ane-N3 ligating units. In this case, only the 1,2-vicinal bimetallic complexes with Cu(ll) ions exhibited high... 

Kimura and coworkers [17], Diamond [18], and Damien et al. [19] have described that the polymeric calix-[4]arenes have been used as ionophores in ion selective electrodes for Na (based on calixarene esters and amides) and for Na and Cs (based on p-alkylcalixarene acetates). The electrodes are stated to function as poten-tiometric sensors as well, having good selectivity for primary ion, virtually no response to divalent cations, and being stable over a wide pH range. 

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