Cryptands Metal complexes

Jean-Marie Lehn et al. Cryptand metal complexes... 

Cryptands, 7, 731-761 alkali metal complexes NMR, 7, 740 reactivity, 7, 743-744 alkaline earth complexes reactivity, 7, 743-744 anion complexes, 7, 747-748 applications, 7, 753-761 as biological models, 7, 753-754 bis-tren... 

H-1,3,2- Diazaborole, 1,2-dihydro-reactions, 1, 641 synthesis, 1, 639, 640 transition metal complexes, 1, 641 Diazadiborine, tetrahydro-semi-empirical calculations, 1, 632 Diaza[2.2.2]cryptand synthesis, 7, 750 Diazacryptands bispyridine... 

Table 7.1. Formation (kf) and dissociation (kd) rate constants for the alkali metal complexes of the cryptands of type (213) in methanol at 25 °C (Cox, Schneider Stroka, 1978).

In the case of allylpotassium, the metal complex exists as a symmetric n structure. No temperature dependence was shown by either 13C NMR for A5[C(i) —C(3)] or by 1H NMR for substitution with deuterium at Cp). Thompson and Ford measured experimentally a variety of allylalkali metal compounds using variable-temperature NMR in THF-dx45. Addends such as TMEDA, hexamethylphosphoric triamide (HMPA), 15-crown-5-ether, [2.1.1]cryptand and n-butyllithium showed either no change in the spectrum or rapid decomposition of the complexing agent. Measurement of the populations of E (17) and Z (18) isomers of 1-isopropylallylpotassium showed the Z isomer to be more stable (Table 11). 

Table 1 Structural Features of Alkali Metal Complexes of [2.2.2]Cryptand (12) <73AX(B)383, 69ax...

The ligand shape has changed and it has inflated on encapsulating the cation. The structures of a large number of [2.2.2]cryptand alkali and alkaline earth metal complexes have been studied by X-ray crystallography.372 Using the criterion that the optimum complexation occurs when the cation and cavity radii are similar, it can be predicted that for this ligand potassium is... 

Gyclodextrin cavities form the early models of host molecules involved in supramolecular assemblies. There are many other molecules known as cryptands which can be designed to offer a cavity of fairly precise dimensions to accommodate various ions or metal complexes. It may be possible to locate not just one, but two, guest molecules inside a cryptand cavity, and this may lead to new electron transfer reactions in restricted environments another step towards synthetic photoinduced biochemical reactions. 

---