Macrotricycles anionic complexes

Macropolycyclic ligands, 2,942 classification, 2,917 metal complexes binding sites, 2, 922 cavity size, 2,924 chirality, 2, 924 conformation, 2,923 dimensionality, 2, 924 electronic effects, 2, 922 shaping groups, 2,923 structural effects, 2,922 molecular cation complexes, 2,947 molecular neutral complexes, 2,952 multidentate, 2,915-953 nomenclature, 2,920 Macro tetrolide actins metal complexes, 2,973 Macrotricycles anionic complexes, 2,951 cylindrical... 

Graf, E., Lehn, J.-M., Anion cryptates-highly stable and selective macrotricyclic anion inclusion complexes. J. Am. Chem. Soc. 1976, 98, 6403-6405. 

A relative of the latter class of compounds are the macrotricyclic quaternary ammonium salts which have been reported by Schmidtchen. The bridges may contain either methylenes or ethyleneoxy units and the nitrogens are quaternarized. The underlying principle is to provide a cavity suitable for solvating or at least trapping anions. Schmidtchen presents evidence which suggests the formation of halide inclusion complexes. The synthesis of these molecules is accomplished along more or less traditional lines Such a species is illustrated above as compound 19. 

A theoretical (AMI molecular orbital) treatment of boron analogues of the katapinand series as well as macrotricyclic compounds related to 16 has also recently appeared. As with the ammonium-based host molecules the macrotricyclic hosts containing four boron atoms exhibited a greater degree of anion specificity as a consequence of the rigidity of their binding sites. In all cases, size selective complexation of halide anions was observed with accompanying decreases in B - B distances and partial sp -> sp rehybridization. ... 

The propagation reaction of ethylene oxide anionic polymerization has been studied in THF at 20 C with " , " + [222], Cs+ and Cs + [TC] as counterions (10,11). [TC] is a spheroidal macrotricyclic tetramine hexaether (25) which forms a very stable complex with Cs+. 

Thus the spherical macrotricyclic molecule represented below gives a tetraprotonated species that has very unusual binding properties. It binds very strongly the spherical chloride anion, holding it in an ideal tetrahedral arrangement of N+—H Cl- hydrogen bonds. This complex is much more stable and the Cl /Br selectivity is much higher than any other known to date. These properties may be attributed to the presence... 

The anion-binding carcerand 11 was described by the Amouri group [31]. This complex contains a tetrafluoroborate anion coordinated to two cobalt(II) ions. Each cobalt ion adopts a square-pyramidal geometry. Four benzimidazole arms of the bridging ligands fill the equatorial positions, and solvent molecules (acetonitrile) coordinate to the outside axial positions. Inside the complex the included tetrafluoroborate anions interacts with the cobalt ions whose inside axial positions are otherwise coordinatively unsaturated. No exchange of the anion was observed even at 60 °C. A detailed study of the anion-binding properties in the crystal state of similar metalla-macrotricyclic cryptands has been performed by Adarsh et al. [32],... 

MD simulations of halide anions [X]- and their inclusion complexes [X] c [L4+] with a macrotricyclic tetrahedral host built from four quaternary ammonium sites dissolved in [C4mim][PF6] were carried out [118]. In the dry IL the uncomplexed halides were surrounded by four to five [C4mim]+ cations which bond via hydrogen bonding to facial coordination. The first solvation shell of [Cl]-, [Br], and [I] comprised of three to four cations next to four H20 molecules for the humid system. The solvation of the [L4+] host and of its [X]-1 [L4+] complex mainly involved anions in the dry IL, and additional H20 molecules in the humid IL. Free energy perturbation calculations predicted that in the dry liquid [F] is preferred over [Cl] , [Br] and [I]- in contrast to the aqueous solution where [L4+] was selective for [Cl]-. In the humid liquid no [F] /[C1] discrimination was observed, showing the importance of small amounts of water on the complexation selectivity [118]. 

After work done by Simmons dealing with catapinands and of Lehn with the soccer ball type cryptand, Schmidtchen described macrotricyclic tetraammonium salts 7, which allow to complex inorganic anions as well as acetate, and more interestingly, biochemical relevant guests like AMP, ATP and NAD... 

Anion cryptates are formed by macrotricycles like (5) in their tetraprotonated state with the spherical halide anions [8]. (5)-4H binds the chloride ion very strongly and very selectively, giving the [Cl" c (5)-4H J cryptate (7), but does not complex other types of anions. These properties are unique at present with respect to both synthetic and natural halide binding sites, very little being known about the latter. Non-complementarity between an ellipsoidal cryptand and the spherical halides results in appreciable ligand distortions in the cryptates formed and in lower binding constants [9, 10] (see also below). 

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