Calixarene complexation

A special class of linked phenols are the so-called calixarenes. Reaction of p-f-Bu-calix[4]arene, abbreviated (FljL), with excess Et2Zn in the presence of TMEDA affords the fully deprotonated calixarene complex Et2Zu5(L)2(TMEDA)2 (168), the structure of which was determined in the sohd state (Figure 84) °. The two cahxarenes are fused by three zinc atoms. One of these is coordinated by two oxygen atoms from each calixarene unit. The other two zinc atoms, connecting the calixarenes, are five-coordinate, bound by... 

Photophysical studies have been conducted on a number of lanthanide complexes of calix[n]arenes, and a significant number of these are discussed in a recent review (79). The first europium and terbium calixarene complexes showed promising photophysical properties, with terbium luminescence lifetime of 1.5 ms and quantum yield of 0.20 in aqueous solution (80). 

FIGURE 4.8 X-ray structure of lanthanide calixarene complex ((La(N03)3)2 (CPw2). 

This difference of behavior of calixarenes bearing CMPO residues either on the wide rim or on the narrow rim was confirmed by extraction of europium (from nitric acid solutions by CPw2 and CPn2 diluted in chloroform) by implementing ESI-MS for the two calixarenes. Complexes with 1 1 and 1 2 Eu calix-CMPO stoichiometry were evidenced. The major species for CPw2 is the 1 2 complex, while for CPn2 the predominant complex is the 1 1 complex.165... 

Bis(butadiene) complexes, with tantalum, 5, 173 Bis(z-butanethiolato) complexes, with bis-Cp Ti(IV), 4, 601 Bis(calixarene) complexes, as organic molecule hosts, 12, 799 Bis(carbene) complexes with gold(I), 2, 287-288 with manganese, 5, 780, 5, 826 with mercury, 2, 429 with palladium, 8, 230 with silver , 2, 206... 

Some Unusual Properties of Crown Ether and Calixarene Complexes... 

Crown ethers continue to be one of the most useful parts of supramolecular chemistry/91 From the beginning computations of metal ions complexes with synthetic ionophores/101 which have been aptly reviewed/111 emphasized the importance of including explicitly solvation in free energy calculations, also with ab initio calculations on calixarene complexes/121 Molecular dynamics simulations of 18-crown-6 ether complexes in aqueous solutions predict too low affinities, but at least correctly reproduce the sequence trend K+ > Rb+ > Cs+ > Na+. However, only the selection of K+ over Rb+ and Cs+ is ascribed to the cation size relative to that of the crown cavity, whereas K+ appears in these calculations to be selected over Na+ as consequence of the greater free energy penalty involved in displacing water molecules ftomNa/1131... 

Schatz, J. (2004) Recent application of ab initio calculations on calixarenes and calixarene complexes. A review, Coll. Czech. Chem. Comm. 69, 1169-1194. 

Synthesis and X-ray crystal structures of the first antimony and bismuth calixarene complexes have been described. The reaction of the monosodium salt of />-/f /-butylcalix[4]arene (BucC4) with 2equiv of SbC provided Bu OKSbCl. Bismuth calixarene complex was prepared by treatment of/>- r -butylcalix[8]arene with Bi[N(SiMe3>2]3 <2004CC1472>. 

Similar behavior is observed for calix[4]arene (see Calixarenes) complexes of the type (89). Moreover, the oxygen donor atoms are particularly appropriate for the oxophilic early transition metals. A rich chemistry has been developed with complexes containing zirconium - carbon bonds. In this area, aryne zirconocene compounds can be thermally generated and isolated withont trimethylphosphane additional coordination. Zirconium-bntadiene chemistry has been explored as well and constitutes a source of zircoiuum complexes. 

Cation-TT interactions, which are frequently encountered in calixarenes complexes, are observed in three related potassium complexes of calix[6]arenes, [K2(MeOH)5] /)-H-calix[6]arene-2H, [K2(MeOH)4] / -t-butylcalix[6]arene-2H and [K2(H20)5] p-H-calix[6]arene-2H. The crystal... 

Coordination geometry of various uranyl calixarene complexes. ... 

One of the important applications of butylcalix[4]arenes arises from their ability to trap alkali metal ions. In particular, Cs+-calixarene complexes have received much attention because of the need to remove the Cs radionucleotide from nuclear wastes. Benevelli et al. have used one-pulse solid state NMR experiments to directly observe Li, Na and Cs ions in the host cavity [52]. More advanced experiments, which allow the investigation of metal lattice interactions were also reported. Rotational-echo double resonance (REDOR) NMR is a useful tool for obtaining structural details of butylcalix[4]arene [53]. Gullion and coworkers used REDOR to determine the position of the... 

The ability of the calixarene complex (12) with its Nbln=Nbln bond to induce four-electron reduction of N2, aldehydes, and ketones has been discussed in Sections 4.5.2.1.2, 4.5.2.2.4, and 4.5.2.4.5.(ii) (Scheme 32). 

In a fifth method (International Reagents Corp., Kokusai-Kobe, Japan), its first reagent contains the detergent cal-ixarene that converts LDL to a soluble complex. Cholesterol esters of HDL-C and VLDL-C are preferentially hydrolyzed by a cholesterol esterase (chromobacterium), cholesterol oxidase, and hydrazine, which divert the accessible cholesterol to cholestenone hydrazone. A second reagent with deoxycholate brealcs up the LDL-calixarene complex, allowing LDL-C to react with the esterase, a dehydrogenase, and P-NAD to yield cholestenone and fi-NADH, the latter measured by a spectrophotometer. 

Ling, J. Shen, Z. Zhu, W. Synthesis, characterization, and mechanism studies on novel rare-earth calixarene complexes initiating ring-trimethylene carbonate. J. Polym. Sci. A Polym. Chem. 2003, 41 (9), 1390-1399. 

Naturally, quantum chemical approaches to molecular recognition are usually employed for selected systems since the complexity of these systems requires a system-specific analysis which makes it difficult to extract results of general validity for examples, see Refs. [13-16] for studies of molecular tweezers. Further examples are mentioned in a review article by Schatz considering ab initio calculations on calixarenes and calixarene complexes [17]. Schatz concludes that although the systems are quite big, useful contributions have been made by ab intio calculations. However, a general model is needed in order to make host-guest processes and template-assisted reactions accessible to a comparison of quantitative measurements and calculations, which may finally provide the basis for rational host design and for the prediction of template effects (compare the recent attempt by Hunter [18]). 

TiO2/SiO2, Ag-Cu alloys, soft Pt(II) Lewis acids, MTO, oxaziridinium salts, NHPI, polyoxometallates, phase-transfer systems, polymer-supported complexes, calixarene complexes, and biologically based systems. 

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