Tris , cryptand

Severin and coworkers reported (146) the reaction of tris(2-aminoethyl)amine and 4-formylphenylboronic acid with penta-erythritol to give, via multicomponent assembly, the boronic acid based macrobicyclic cage 35 (Fig. 25). The cage has the form of an ellipsoid with a diameter of 20.5 A and binds two Cud) ions in a fashion similar to the smaller tren-based cryptands. The reversible formation of boronic esters has also been employed to build other hollow structures such as nanotubes (147) and porous covalent organic frameworks (148,149). 

The fluorescence spectrum of the tris-acridine cryptand A-13 shows the characteristic monomer and excimer bands. Upon complexation with various organic anions (carboxylates, sulfonates, phosphates), the monomer band increases at the expense of the excimer band. The stability of the complexes depends on the contribution of the electrostatic and hydrophobic forces and on the structural complementarity. Stability constants of the complexes ranging from 103 to 107 have been measured. In particular, A-13 binds tightly to mono- and oligonucleotides, and it can discriminate by its optical response between a pyridimic and a purinic sequence. 

As seen in Figure 14 the ellipsoidal cryptands may be prepared by the simultaneous formation of three bridges. This route has found limited use due to low yields but has been employed in the synthesis of some cryptands including the tris-pyridino system (36) (81TL3035) and bis-tren (18) (80UP52100). 

Numerous macrocyclic and macropolycyclic ligands featuring subheterocyclic rings such as pyridine, furan or thiophene have been investigated [2.70] among which one may, for instance, cite the cyclic hexapyridine torands (see 19) [2.39] and the cryptands containing pyridine, 2,2 -bipyridine (bipy), 9,10-phenanthroline (phen) etc. units [2.56,2.57,2.71-2.73]. The [Na+ c tris-bipy] cryptate 20 [2.71] and especially lanthanide complexes of the same class have been extensively studied [2.74, 2.75] (see also Sect. 8.2). 

Macrobicyclic cascade cryptands have also been prepared such as the series of bis(tren) derived (tren = tris(2-aminoethyl) amine, see Section 4.4.3) compounds 5.9. The di-nickel(II) and di-copper(II) complexes of the cages with various spacers all bind a metal cation into each tren unit. These metal... 

Tse-Lok Ho 3I) has explored the effectivness of the following four nucleophiles in dequatemization reactions sodium azide, sodium thiosulphate, thiourea and tri-phenylphosphine. Among.which, triphenylphosphine turned out to be the most effective demethylating agent. A strong solvent dependence on dequatemization has been demonstrated, indicating dimethylformamide as a superior solvent in all cases. In this manner, (2B.2.1]cryptand (44) was obtained from bisquaternary salt 43 in 87% yield (Scheme 11). 

Bridging with tri-functional reagents in 1,3,5-position at the wide, or at the narrow rim led to a more or less rigid skeleton. In such a series of 1,3,5-bridged calix[6]arenes 84 chirality is caused by the CTV moiety used as bridging element.157,158 The calix[6]cryptands 85a and 85b on the other hand are inherently chiral due to the 1,2,4-tri-substitution pattern on the narrow rim.159... 

Cryptand = 4,7,13,16,21,24-hexaoxa-l,10-diazabicyclo [8.8.8]hexacosane Ind = ) -indenyl Trmpe = 1,1,1-tris (dimethylphospliinometliyl)etliane tritox = (f-Bu3C)3CO . 

Suitable cryptands have been used to increase greatly the rates of reactions where F , Br , P, OAc, and CN are nucleophiles." Certain compounds that are not cryptands can act in a similar manner. One example is the podand tris(3,6-dioxaheptyl)amine (103), also called TDA-1." Another, not related to the crown ethers, is the pyridyl sulfoxide 104." " ... 

Af-Phenylbenzylhydroxamic acid [24] and crown ethers [25] were applied for the extraction of Zr. Zirconium has been extracted from transition metals with the use of [2.2.2]-cryptand in CHCI3 [26]. Zr (HO has also been extracted with tris(2-ethylhexyl) phosphate [27] and dibutyl sulphoxide (in xylene) [28]. 

Neutral Ti(CO)6 is an extremely unstable compound which decomposed even below -220 °C, as shown by matrix isolation spectroscopy [165]. The much more stable phosphine derivatives Ti(CO)3(dmpe)2, Ti(CO)5(dmpe), Ti(CO)5(PMe3)2, Ti(CO)4(PMe3)3 have been isolated [166-168]. In contrast, the dianionic salt [Ti(CO)6] (53) is thermally much more stable and decomposes only above 200 C. Complex 53 was obtained by reductive carbonylation of Ti(CO)3(dmpe)2 by alkali metal naphthalenides in the presence of cryptand [169]. Carbonylation of 79 also produces 53 [170]. The naph-thalenide-assisted reductive carbonylation of the zirconium tetrachloride afforded the zirconium analog [Zr(CO)6] (54) [171], which was also derived by carbonylation of the tris(diene) dianion 45 [150]. One anion [R3Sn] effectively stabilizes Ti(CO)e as an air stable monoanionic salt, [R3SnTi(CO)J [172]. 

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