Calix arene 4- complex

Two other types of host for arenediazonium salts were found by Shinkai et al., the calix[ ]arenes, 11.10 (1987 a, 1987 b) and 11.11 (1988). The hexasulfonated calix[6]arenes 11.10 suppress dediazoniation of substituted benzenediazonium ions in aqueous solution much more efficiently than 18-crown-6. The complexation of calix[ ]arenes 11.11 (n = 4, 6, and 8) with 4 -dimethylaminoazobenzene-4-diazonium ions (11.12) was measured, and was found to be weaker than that of 18-crown-6. It may be that the large difference in behavior between these two types of complexation reagents 11.10 and 11.11 is due to the significantly different diazonium ions used as guests for the two types. Electronically the azobenzenediazonium ion (11.12) is... 

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. 

The tantalum(V) calix[4]arene complex 44 provides an interesting scaffold for the construction of an j -PhC2C=CPh ligand upon reaction with an excess of phenylethynyllithium (Scheme 10). The coupling reaction is presumed to proceed via bis-alkynyl 45, which is subsequently attacked at the a-carbon of one of the acetylide ligands to give anion 46, isolated as its lithium salt. The addition of a further equivalent of LiC CPh is probably prohibited by orbital constraints. ... 

Xu, W., Vital, J. J., Puddephatt, R. J., Selective anion inclusion in calix[4]arene complexes driven by face-bridging mu-4 halide binding. J. Am. Chem. Soc. 1993, 115, 6456-6457. 

Corazza, F., Floriani, C., Chiesi-Villa, A., Guastini, C., The oxo-molybdenum(Vl) group over a calixarene-oxo surface— calix[4]arene complexing inorganic and organic functionalities. J. Chem. Soc., Chem. Commun. 1990, 640. 

Calix[ ]arenes are a family of macrocycles prepared by condensation reactions between n /v/ra-substituted phenols and n formaldehyde molecules under either base or acid catalysis. Different sizes of the macrocycles can be obtained (n = 4-20) (Stewart and Gutsche, 1999) depending on the exact experimental conditions, which were mastered in the 1960 s (Gutsche, 1998), but the most common receptors are those with n =4,6,8 (macrocycles with an odd number of phenol units are more difficult to synthesize). We use here the simplified nomenclature in which the number of phenolic units is indicated between square brackets and para substituents are listed first.4 Calixarenes, which can be easily derivatized both on the para positions of the phenolic units and on the hydroxyl groups, have been primarily developed for catalytic processes and as biomimics, but it was soon realized that they can also easily encapsulate metal ions and the first complexes with d-transition metal ions were isolated in the mid-1980 s (Olmstead et al., 1985). Jack Harrowfield characterized the first lanthanide complex with a calixarene in 1987, a bimetallic europium complex with p-terf-butylcalix[8]arene (Furphy etal., 1987). 

The structural characterization of a mononuclear Eu-calix[6]arene complex reveals a more unusual complexation mode. In Eu(H4LXOHXDMF)6 (H6L = p-tm-butylcalix[6]arene Table 13) the Eu cation is placed outside the cavity forming only one monodentate bond to the calixarene ligand [193]. Six DMF molecules and most likely a hydroxyl group accomplish 8-coordination. The smaller sized calix[4]arene [194] and ether-extended bis(homooxa)-p-tert-... 

A homobimetallic cerium(IV)-calix[8]arene complex was used together with hydrogen peroxide in the regioselective hydroxylation of simple phenols (Eq. 38), Just 0.5 mol of the cerium complex was sufficient to convert 1 mol phenolic substrate [260],... 

The corresponding dependence of cation complex stability on the anion differs profoundly from that of most other cation receptors such as cyclophanes or calix-arenes [16]. For these cation complex stability decreases on changing the anion from picrate through iodide to tosylate, a dependence that has been attributed to ion-pair aggregation in non-polar solvents. Because the interaction of quaternary ammonium ions with tosylate or iodide in chloroform is considerably stronger than with picrate, cation complexes in the presence of the latter anion are usually more stable. Only when iodide or tosylate cooperatively contributes to cation binding, as in 3 or in some recently described calixarene derivatives [17], is reversal of this order observed. 

Rondelez Y et al (2002) The first water-soluble copper(II) calix[6]arene complex presenting a hydrophobic ligand binding pocket a remarkable model for active sites in metalloenzymes. Angew Chem Int Ed Engl 41 1044-1046... 

Molenveld P et al (1999) Dinuclear and trinuclear Zn(II) calix[4]arene complexes as models for hydrolytic metallo-enzymes. Synthesis and catalytic activity in phosphate diester transesterification. J Org Chem 64 3896-3906... 

Other signiflcant complexes of this type, containing one or more lanthanides, are formed by calixarenes (see Calixarenes) Much of this work has been prompted by their potential in separating lanthanides from uranium and other metals. A calixarene ligand with two amide substituents has been synthesised as an extractant for lanthanides dimeric Sm and Eu and monomeric Eu complexes have been prepared. Another calixarene, with four phosphine oxides attached, has been fixed to silica particles and the resulting system has been found to give very efficient extraction of Eu + and Ce + from simulated waste. A calix[4]arene complex of Gd + binds... 

Beer, P.D., Szemes, F., Passaniti, P., and Maestri, M. (2004) Luminescent ruthenium(II) bipyridine-calix[4]arene complexes as receptors for lanthanide cations. Inorganic Chemistry, 43, 3965... 

The structure of a di-/i-oxo bridged calix[3]arene complex has been reported whilst other complexes have been isolated with p-t-butylcalix[n]arenes n = 4,6,8). p-t-Butylcalix[4]arene forms a 2 1 complex whilst p-t-butylcalix[6]arene and p-t-butylcalix[8]arene form 1 1 complexes, but these compounds at present lack structural characterization. " ... 

The macrocyclic calix[4]arene complex (Ti(Bu -calix[4]arene))2 was prepared from Ti(NMe2)4 and the neutral ligand. One of the four O atoms of each ligand bridges the two titanium centers.673 The related complex TiCl(But-calix[4]arene(0Me)(0)3) (61) was synthesized by a salt metathesis reaction. Subsequent displacement of the Cl by alkyl or aryl groups was readily accomplished.674... 

By reducing the tetravalent [K(DME)]2[(Et8-calix-[4]-tetrapyrrole)Th(/i-Cl)]2 with K(naphthalene), it was possible to obtain a unique example of the Th arene complex [(Et8-calix-[4]-tetrapyrrole)ThK(DME)](/i,/i -774 76-GioH8)-(fi-K) . Exposure of a deep red toluene solution of the naphthalene complex to C02 at room temperature... 

Reaction of silsesquioxane RySiyO OH (R = c-C6H11, C-C5H9) with Ti(CH2Ph)4 in toluene or diethyl ether occurs with protonolysis to give the monoalkyl derivative Ti(CH2Ph)[R7Si709(0)3] (Scheme 2).15-17 Monoalkyl calix[4]arene complexes shown in Scheme 3 have been synthesized. The molecular structure of the phenyl compound has been determined by X-ray diffraction methods.18... 

The mono-Cp calix[4]arene complex shown in Scheme 385 has been synthesized by the reaction of the parent chloro compound with NaCp the molecular structure has been determined by X-ray diffraction methods.919... 

Use of molecular mechanics to model a dynamic process Bis(calix[4]arene) complexes of K+... 

Catalytic HPNP-tranesterification reactivity (Fig. 40, bottom has been reported for zinc complexes assembled using calix[4]arene ligands (Fig. 65).172,248 251 Complex 9 induces a 23,000-fold rate enhancement over the uncatalyzed intramolecular cyclization reaction of HPNP.248 Kinetic and mechanistic studies indicate strong binding of the HPNP substrate to the complex (K— 5.5 x 10-4M-1) and a kc ll value of 7.7 x 10 4s 1 at pH = 7.0 in acetonitrile/20 mM HEPES (1 1) at 25 °C. As 9 is 50 times more active for HPNP transesterification than 8, which contains only one zinc center, cooperativity between metal centers occurs in the former complex. Notably, the monozinc calix[4]arene complex 8 is 6 times more reactive than 7. This result provides evidence that the hydrophobic calix[4]arene moiety plays an important role in the reaction. 

Flexibility is important in term of the HPNP reactivity of the calix[4]arene complexes, as evidenced by the fact that the constrained analog 11 (Fig. 65) exhibits both a lower substrate affinity (K = 0.70 x 10-4M-1) and catalytic rate (fccat = 0.95 x 10 4s 1) than 9.249... 

Fig. 65 Calix[4]arene complexes examined for HPNP-transesterification reactivity.

Fig. 67 Proposed mechanism for HPNP transesterification catalyzed by a trinuclear (N3Zn)3-appended calix[4]arene complex. The calix[4]arene unit is not shown for clarity.

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