Macrobicycles anionic complexes

In macrobicyclic cryptate complexes where the cation is more efficiently encapsulated by the organic ligand these ion pair interactions are diminished and the reactivity of the anion is enhanced. This effect is seen in the higher dissociation constant, by a factor of 104, of Bu OK in Bu OH when K+ is complexed by [2.2.2]cryptand (12) compared to dibenzo[18]crown-6 (2). The enhanced anion reactivity is illustrated by the reaction of the hindered ester methyl mesitoate with powdered potassium hydroxide suspended in benzene. 

A cryptate effect is observed for anion complexes as is the case for cation complexes (Section 2.3). In general, an increase in cyclic order from acyclic to macro-cyclic to macrobicyclic significantly increases the stability and selectivity of the anion complexes formed by polyammonium ligands. 

Successful anion complexation was also achieved with larger macrobicyclic ligands. Thus, the macrobicycle 17 (Fig. 17). SI binds halide anions and the linear triatomic azide anion with a very high stability constant. The x-ray structure revealed an efficient shape and size complementarity between N3 and the cavity. A whole series of polyazacryptands was obtained in high yields by a simple Schiff base [2 + 3] condensation between the triaminotriethylamine (tren) and various dicarboxalde-hydes. The hexaimine macrobicycles prepared by this way lead, after reduction, to the polyaza cryptands, which in... 

Dietrich, B., Dilworth, B., Lehn, J.-M., etal, Anion cryptates Synthesis, crystal structures, and complexation constants of fluoride and chloride inclusion complexes of polyammonium macrobicyclic ligands. Helv. Chim. Acta 1996, 79, 569-587. 

The BF4 anion in the clathrochelate [CoDma(BF)2](BF4) complex can readily be replaced by another large inorganic anion (e.g. PFe ) via an exchange reaction occurring in aqueous-acetonitrile solution in the presence of a great excess of the substituting anion salt [39]. The reduction of the [CoDma(BF)2](BF4) clathrochelate with Nal solution in acetone yielded a macrobicyclic cobalt(II) CoDma(BF)2 complex. The synthesis of the latter via a template condensation on the Co2+ ion was not yet successful. 

Phosphorus-containing tris-diimine d-metal complexes are isolated as ionic associates with a bulky inorganic BF4 anion and readily crystallize. Therefore, monocrystals of these compounds, suitable for X-ray analysis, were obtained, and X-ray crystallography - the major method for determining their geometry - was applied to all complexes of this type. The subtle features of the electronic structure of macrobicyclic phosphorus-containing d-metal tris-diiminates have been examined by a variety of spectral methods and quantum-chemical calculations. 

Except for A-[Co(diNOsar)]3+ cation, all the changes in CD spectra due to ion pairing are in such a direction that they enhance the Ea rotational strength. This type of CD changes is characteristic of complexes with D3 symmetry and indicates the association of an anion in the equatorial plane. This inference coincides exactly with the deduction from the structural features of macrobicyclic... 

For the macrobicyclic [Co(sep)] + cation in different solvents and with various anions, the photoeffect enhances in the order H2O < CHsOH < Br < r < HC204 . For the [Co(sep)](B(C6H5)4)3 complex, the photoeffect increases with decreasing solvent polarity that makes the bond between the cation and the anion or a solvent more stable. 

Optically active macrobicyclic complexes may be employed as chiral eluents for the separation of optically active anions (Section 5.1) and as chirality probes for biological objects [307, 310, 312],... 

The macrobicyclic cryptand BISTREN (3), as discussed earlier, binds anions when hexaprotonated. This compound is also capable of binding pairs of transition metal ions [e.g. the bis-copper(Il) Complex (55)] when unprotonated (39, 138). The bis-copper(II) based receptor (55) was observed to bind a chloride ion cascaded between the two metal ions. In fact, receptor 55 bound chloride more strongly (log K = 3.55) than the hexaprotonated form of 3 (log K = 2.36), and this was attributed to the formation of strong coordinate bonds. Hydroxide was also cascade bound forming a thermodynamically very stable complex (log K = 11.56), the resulting complex being of a different type from that formed by non-cryptate complexes of the Cu(II) ion. 

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