Polyether macrocycle

Fig. 21. Dendritic polyrotaxanes with mechanical branching units containing covalently linked bis-dendrons and a core imit fused to polyether macrocycles...

Crown polyethers. Macrocyclic effects involving complexes of crown polyethers have been well-recognized. As for the all-sulfur donor systems, the study of the macrocyclic effect tends to be more straightforward for complexes of cyclic polyethers especially when simple alkali and alkaline earth cations are involved (Haymore, Lamb, Izatt Christensen, 1982). The advantages include (i) the cyclic polyethers are weak, uncharged bases and metal complexation is not pH dependent (ii) these ligands readily form complexes with the alkali and alkaline earth cations... 

A series of polyether macrocycles [59]—[66] (Fig. 33) that contain a coordinated reducible, redox-active 16-electron molybdenum nitrosyl (Mo(NO)(3+ group have been prepared (Al-Obaidi et al, 1986 Beer et al., 1987). Compounds [59]—[63] were synthesized from the reactions between [Mo(NO)LX2] (L = tris(3,5-dimethylpyrazolyl)hydroborate X = Cl or I ) and the appropriate amine substituted benzo-crown ether. Compounds... 

The 20-crown-6 derivative (5)-207 (61), which contains a 3,3 -dimethyl-l,r-dinaphthyl unit bound to the polyether macrocycle through its 2,2 positions, both in its free form and bound to Me3CNH cations. 

In addition to attempts at constructing ion channels on the basis of multicon-nected polyether macrocycles [8.193], we have investigated mainly two approaches... 

Bouquet -shaped molecules based on either a polyether macrocycle [8.205] or a /3-cyclodextrin (/3-CD) [8.206] core, such as 114 and 115 respectively, have been synthesized and their polycarboxylate forms have been incorporated into vesicle bilayer membranes [8.207]. They present structural features suitable for studies of chundle-type molecular channels (1) the functionalized cyclic annulus possesses substrate selection properties (2) it bears axially oriented bundles of oxygen-containing chains, which provide binding sites for metal cations and are long enough for the molecule to span a typical lipid membrane (the overall length with the chains... 

A great variety of polyether macrocycles, containing from 3 to 20 oxygen atoms and with ring sizes from 9 to 60, have been prepared by Pedersen (105-108). The synthetic routes used in cyclic polyether formation all require NaOH, but a template role for the Na+ ion has not been established ... 

The lariat ethers comprise a snbset of the polyether macrocycles, and are identified by their pendant chains. They can be categorized as either N-pivot (19) or C-pivot (20), depending on which type of atom the chain is attached. As for their polyether parents, much of the focus on these macrocycles has been on complexation of alkali and alkaline earth metal ions. 

Polyether macrocycles (18) are the simplest of the polyoxa macrocycles. The commonly used name for these macrocycles is the crown ethers, due to their crown-like structure in the solid state. These molecules have been extensively studied... 

The consequences of increasing the size of the polyether macrocycle to 68 members (that is, by a factor of two over the small ring system) was investigated. Accordingly, the synthesis of tetrakis-/ -phenylene-68-crown-20 was achieved in dimethylformamide at room temperature in excellent yield and this, in turn, was initially used to produce the [2]-catenane 22 (Figure 5.13). From the temperature dependence of the H NMR spectrum, 22 appears to behave like a molecular train - with the tetracationic cyclophane travelling from station to station around the... 

The presence of a polyether macrocycle or cryptand adapted to the size of the alkali cation [10] facilitates the reduction of molecules which are otherwise difficult to reduce by the alkali metal it stabilizes and solubilizes the reduced molecules and induces the formation of crystals. Li+ salts are stabilized by the presence of 12-crown-4 or 2,2,2-cryptand Na+ salts are stabilized by 12-crown-5 or 2,2,2 cryptand and K+ salts are stabilized by 18-crown-6 [10, 35], for example ... 

Aryl-ether-based dendrons were used as stoppers in a series of rotaxanes containing one to three bipyridinium units surrounded by polyether macrocycles (compounds 74-76) [150], Electrochemical investigation in acetonitrile shows that a first reversible cathodic wave is due to the bipyridinium units, which are all reduced simultaneously and independently at the same potential. Electrode adsorption problems prevented accurate measurements for a second reduction process, also due to the bipyridinium units. On oxidation, two not fully reversible processes are observed, involving both the polyether macrocycle surrounding the bipyridinium units and the dioxybenzene units of the dendritic stoppers. 

A very recent class of ligands (2002) is based on a lanthanide phthalocyanine moiety which links one or four polyether macrocycles (154) they show different aggregate forms under various conditions, i.e., the cation present or the solvent used.248... 

Dendrons have also been used as the capping moieties for rotaxane cores (Figure 8). Amabilino et al. reported the Williamson coupling of the third generation Frechet-type dendrons 6 to cap polyether macrocycles threaded around linear bipyridinium oligomers.241 When the linear component consisted of multiple viologen units, 171, shuttling of the... 

Although they have been developed primarily for use with alkali and alkaline-earth ions (see page 200), it is appropriate to mention here the polyether macrocycles. These are of two main types (1) monocyclic ones,7 such as (21-XXV1), and (2) the bicyclic molecules,8 such as (21-XXVII). These compounds are remarkably powerful complexing agents for alkali and alkaline-earth ions, giving unusual coordination geometries.9 There is as yet no detailed report of their complexes with other metal ions. 

Lastly, a convenient fcw-crown ether derivative of triaminotriazine, prepared from a phthalic acid derivative of a polyether macrocycle, would make an excellent reagent in the preparation of dendrimers desirous of surface crown ether(s) <97BCSJ671>. 

In an example that illustrates supramolecular weaving , Stoddart and coworkers found that in the X-ray structure of the 1 2 complex 55 between BPP34C10 53 and the ammonium salt 54, the two cations are threaded co-direc-tionally through the centre of the macrocycle (Scheme 11b) [51]. This arrangement is stabilised by a total of six N -H- -O hydrogen bonds between the two NH2 centres and three oxygen atoms from each polyether macrocycle (N- -O... 

Liquid-liquid extraction techniques are used in some cases for the industrial separation, concentration and recovery of metals. Introduction of sulfur into the polyether macrocycles has increased the selectivity of those compounds toward the thiophilic metal ions such as Ag", Hg , Au" and Pd" . 

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