Calix arene tetraesters

C. Perez-Jimenez, S. J. Harris, and D. Diamond, A novel calix[4]arene tetraester with fluorescent response to complexation with alkali metal cations, 7. Chem. Soc., Chem. Commun. 480(1993). 

A suitable binding site for metal ions can often be prepared by functionalization of the lower rim of calixarenes with simple ligands. For instance, calix[4]arene tetraesters are good complexants of mono- and divalent ions [391], Valeur et al. have exploited this property in the synthesis of 58, which has the... 

Shinkai s 38113 is also a PET system whose fluorescence is controlled by Na+ binding to a coordinatively active spacer which is a calix[4]arene tetraester in this case. However, the through-space distance between the photoactive termini is expanded by Na+ complexation, thus reducing the PET efficiency. Kuhn s 3993 is not dissimilar in that a PET-type quencher (a nitroaromatic unit) is held away from the lumophore by Ca2+ binding. However a conventional lumophore-spacer-receptor is also contained within 39 as found in 24. At this point it would not be out of place to mention several important studies on the control of PET/EET by ion binding to a coordinatively active spacer between photoactive terminii.114-117 System 36 is structurally related to Verhoewen s 40118 since they both contain an aromatic lumophore and an aromatic amine with one or more interposed aliphatic amines. System 40 also displays the functional similarities that PET processes were... 

Alkali cations have also been involved in two interesting photophysical studies concerned with PET processes. In the first of these, sodium ion com-plexation to a diazacrown ether spacer between a PET donor-acceptor pair causes an acceleration of the electron transfer supporting a superexchange interaction [129]. The second case relies on sodium ion induced conformational changes in a calix[4]arene tetraester diagonally substituted with a PET donor-acceptor pair [130]. This results in a good fluorescent sensory action. 

Relatively few molecular separations have been studied from the utilitarian standpoint. One of these, the purification of fullerenes via 8 , is discussed on p. 170. In a reciprocal experiment the separation of 4 " , 6 , and 8 with a column using a chemically-bonded C o silica stationary phase has been re-ported. Chromatographic selectivity has been achieved for amino acid esters and alkali metal cations on silica-bonded calix[4]arene tetraesters, the structure of which has been explored by and Si-CP-MAS NMR. Silica-bonded calixarenes have also been used as packing materials for HPLC columns that are capable of separating disubstituted aromatics, peptides, and nucleosides. The HPLC separation of phenols using 6 ° as a constituent of the eluent has been described. ... 

Recognition of ion-pair species can be achieved using a calix[4]arene tetraester functionalized with the Re(i) bipyridyl fragment. The oxygen-rich lower rim of the macrocycle in 145 was designed to act as a cation-binding site. 

Israeli, Y. Detellier. C. Complexation of the sodium cation by a calix[4]arene tetraester in solution. Formation of a 2 1 calixarene sodium complex. J. Phys. Chem.. B 1997. 101. 1897-1901. 

We synthesized receptors 26 and 27 which consists of both a uranyl containing salen part for the complexation of the anion and a crown ether or a calix[4]arene tetraester based ionophore for the complexation of the cation [ref 33]. They have been prepared from the corresponding disaldehydes, cw-l,2-diaminocyclohexane and U02(0Ac)2 2H20 in refluxing alcohol. The complexation of the bifunctional receptors with cations and with anions was investigated by NMR spectroscopy, cyclic voltammetry, FAB-spectrometry, and liquid-liquid extraction experiments. 

Early contributions in this area came from Reinhoudt s group and refer to cases in which the ion-pair-binding mechanism is of the host-separated type (Figure 19c) (for original references see reviews ). They first exploited cone calix[4]arene tetraesters or 1,3-alternate calix[4] crowns as binding units for alkali metal ions and uranyl-salophen complexes as anion-binding sites. 

For instance, receptor 76b shows selectivity toward NaH2P04, as a consequence of the sodium-selective complexation at the lower rim by the cone calix[4]arene tetraester and the selective inclusion of H2P04 at the upper rim, as previously found for the analogous receptor l(i2kP Compound 77, acting as heteroditopic carrier, is able to transport the hydrophilic CsCl better than the more lipophilic CsNOs across a SLM, owing to the higher... 

The model has been verified experimentally for the transport of alkali metal cations (27) mediated by valinomycin (1), dibenzo-18-crown-6 (2) and calix[4]crown-5 derivative 3 and calix[4]arene tetraester derivative 4 (Chart 1). D , and for the transport of guanidinium ion (22, 23) mediated by calix[6]arene derivatives have been obtained as well. 

Fig. 2. Response of liquid-membrane electrodes based on 1(a), 2(b), 3(c) and 4(d). These were the first results demonstrating the selectivity of ISEs based on calix[4]arene tetraester and calix[6]arene hexaester derivatives. The tetramers are cleaily sodium selective and the hexamers caesium selective. Taken from reference [2] with permission.

Recently, Shinkai et al. reported that the 1,3-altemate conformer of calix[4]arene tetraester can form both a 1 1 and a 2 1 metal/calixarene complex and the two metal-binding sites display negative allostericity by H-NMR titration [26]. In the present systems, due to the existence of two metal-binding sites there are several possibilities for metal complexation modes, as shown in Figure 5. Thus, a 1 1 and a 2 1 metal complexation of both hexaethyl ester 3 and octaethyl ester 4 might be possible. 

Diamond and coworkers attribute an increase in fluorescence from the anthracene reporter sites of 44 to the increased rigidity induced by complexation of Li+, Na+, and K+ to the calixarene s tetraester cleft. The tetraamide derivative, 45, shows an especially selective response to Na+ ion [383], Restricted motion of the calix[4]arene is believed to lead to the enhanced luminescence response. This contention is supported by H NMR studies, which show metal ions to confer significant order on the calix[4]arene receptor. 

Less is known about tetraesters of calix[4]arenes . Tetrabutanoates in partial cone, 1,2- and 1,3-alternate conformation have been obtained from 2a °, while aU four isomers are known for the tetraacetates. The tetratosylate (or p-bromophenylsulphonate) was used as protective group while modifying substituents in the p-position, and derivatives in the and 1,3-alternate conformation have been obtained in excellent yield,... 

The reactions of calix[4]arenes with acyl or aroyl halides in the presence of AICI3 yields either the tetraester (i.e. with 4 )28s qj. A,C-diester (i.e. with mono-p-(cyanomethyl)calix[4]arene, the difference being attributable either to the p-substituent and/or the solvent (CH2CI2 in the first case CH2CI2/DMF in the second case). With mono-p-(cyanomethyl)calix[4]arene 122 the diben-... 

Figure 2,40 A direct infusion ESI mass spectrum of a tetraester calix[4]arene molecule with sodiated molecular ion at 1016 m/z (The inset mass spectrum shows the fragmentation of the 1016 peak - yielding a daughter ion at 929 m/z representing loss of the most weakly held ester group (87amu) from the tetraester). The predominant ion in the spectrum is that of the diester (structure shown) since this compound forms a strong sodiated adduct in the MS.

Zetta. L. Wolff. A. Vogt. W. Platt, K.-L. Bohmer. V. Asymmetrically substituted calix[4]arenes A two-dimensional proton NMR study of a tetraester derivative in the cone conformation. Tetrahedron 1991. 47. 1911. 

Calix[4]arenes 5 can be converted to the tetraester derivatives by reaction with ethyl bromoacetate in the presence of NaH as a base. Interestingly, while 5a provided the corresponding cone conformation as the sole product (62 % yield), 5b gave a mixture of the cone (34 %) and the partial cone (30 %) conformations. This indicates rather unexpected influence of para-substituents (methyl versus isopropyl) on the conformational outcome of the alkylation reaction [1,2]. 

Replacement of the Phenolic OH Groins. Recendy the synthesis of completely dehydroxylated calix[4]arene 14d by reductive cleavage (K in liquid ammonia) of the tetrakis(diethyl phosphate) ester of p-tert-butylcalix[4]arene 9b has been reported [13]. Starting from the 1,3-di- and tetraesters of 9b we could isolate the partially dehydroxylated calix[4]arenes 14a-c [14]. 

These tetraesters are used in the reaction with upper rim functionalized calix[4]arene derivatives, which will be published elsewhere. 

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