Metalation 9-alkylated calix arenes

III. Metalation of Calix[4]arenes and O-Alkylated Calix[4]arenes... 

METAL ATI ON OF CALIX[4]ARENES AND O-ALKYLATED CALIX[4]ARENES USING TRANSITION METALS... 

Thus, the characteristic potentiometric selectivity of calix[6]arene hexaester 29 for primary amine guests can be reasonably interpreted on the basis of the structural factors relevant to the nonpolar moieties of guests. Such a mode of discrimination can also be achieved by a calix[6]arene hexaester with short alkyl chains [28 (R = H)]. In addition, the selectivity was found to be essentially the same in the presence or absence of lipophilic anionic site HFPB added in the membrane (Table 3). Potentiometric discrimination of protonated amines by host 28 (R = H, Bu ) as well as of aldehydes (as the protonated hydrazones generated in situ) by hosts 26 (R = Bu ) and 28 (R = H) was also reported. Recently, quantitative estimation of optical selectivities for alkali metal ions or protonated amines were made with liquid membranes containing chromogenic derivatives of calixarenes. ... 

The two calix[4]arenes, 24 and 26, are examples of useful derivatives the former binds lanthanides to form luminescent complexes, the latter, prepared from compound 25, is water soluble and crystallizes in a variety of forms, from laminates to nanospheres. Other derivatives are to be found in the literature. Simple derivatives, such as the O-alkyl compounds, are used as a basis for upper rim functionalization treatment of these compounds with nitric acid replaces the upper f-butyl groups with nitrates. Nitrocalixarenes can be reduced to the corresponding amines to generate a platform for further extension of the cavity and have been used to bind metals or small molecules. Oxa- and azacalix[3]arenes represent crown ether-calixarene hybrids and have binding modes reminiscent of both classes of molecules. Many alternative upper rim substituents can be introduced and, in the case of the azacalixarenes, the /V-substituent can easily be varied. 

Inspired by the strong ability of calix[6]arene 1 in complexation of alkali metal ions [4, 8-10], Nomura et al. (1991, 1993) reported that calix[6]arene derivative 1 was an effective catalyst for the esterification reaction of alkyl halide and alkali metal carboxylates (see Fig. 27.3, and Table 27.2) [11, 12]. In order to assess the role of calix[6]arene in the reaction, it needs to take a look the skeleton of calix[6] arene 1. Calix[6]arene 1 contains a hydrophobic aromatic groups and a hydrophilic trioxadecyl functionality. These groups commit calix[6]arene 1 into an octopus-type shape, and indeed this shape provides conformational and structural mobility that brings out a highly efficient catalyst. Similar phase-transfer catalysts... 

In order to confer the calixarenes the ability to form SAMs on metal surfaces, they have to be chemically modified to introduce chemical functions (e.g., thiol, thioether, disulfide) able of chemisorption on the surface. Reinhoudt published the synthesis of calix[4]arenes bearing four di- -decyl sulfide chains at the lower rims. The synthesis proceeds via first the alkylation of the calix[4]arene-25,26,27,28-tetrol with 10-undecen-l-yl tosylate followed by the anti-Markovnikov addition of 1-dodecanthiol in the presence of 9-borabicyclo[3.3.1]nonane (9-BBN) (Fig. 37.11) [64]. Similarly to calix[4]arenes, resorcin[4]arenes tetrasulfides have been produced by the condensation reaction of resorcinol and 11-undecylenic aldehyde followed by the addition of 1 -dodecanthiol to the terminal double bonds of the alkyl chains using catalytic amounts of 9-BBN [63]. 

By changing the nature of the base and the solvent a certain control of the stereochemical outcome has been achieved in few alkylation [15] and acylation [24] reactions of calix[4]arenes. Recently, in collaboration with the group of Prof. D.N. Reinhoudt, several stereoisomeric calix[4]arene crown ethers have been synthesized and their ionophoric properties toward alkali metal cations determined by the Gam s extraction method [25]. In all cases it was found that these ligands are very selective for potassium cation and that the compounds in the partial cone structure are more efficient and more selective than those in the fixed cone conformation. The highest difference in... 

The reaction of calix[4]arene 9b with tetraethylene glycol ditosylate gave the caUxerown ether 25 in 53 % yield [24]. Subsequent alkylation afforded the 2,4-di-alkylated calixcrowns 26 in mixtures of the cone, the partial cone and in some cases the 1,3-altemate conformations, except for the dimethyl ether 26a, which is flexible and adopts the cone conformation. These alkylated calixerown ethers form complexes with alkali metal ions and all of them are selective for K+. The partial cone is not only the best conformation for complexation, which was nicely illustrated by compound 26a, which changed from a cone to a partial cone conformation upon complexation of a cation, but also shows the highest selectivity for K . The dinriethyl ether has been applied in a K -selective electrode based on ISFET-technology [25] and in supported liquid membranes that are used for the selective transport of K [26]. 

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