A GENERAL-METHOD FOR THE DETERMINATION OF THE KINETIC STABILITY OF MACROCYCLIC ALKALI-METAL COMPLEXES WITH RATES OF DECOMPLEXATION BELOW 10(-3) S(-1)

A general method has been developed for the determination of kinetic s tabilities of macrocyclic alkali-metal complexes with rates of decompl exation (k(d)) below 10(-3) s-1, by use of radioactive isotopes. This method offers the possibility to study the influence of the solvent po larity and of the salt concentration in solution on the rate of decomp lexation of macrocyclic metal complexes. Further advantages are the sm all amounts of ligand required for these determinations and the simpli city of the method. Furthermore, it is possible by this method to stud y the 'degenerate' exchange of sodium for sodium and of rubidium for r ubidium. By this method the kinetic stabilities of the sodium and rubi dium complexes of calixspherands 1-4 were determined. Calixspherand 3 forms kinetically very stable complexes with sodium and rubidium catio ns in acetone and Me2SO in the presence of high concentrations of sodi um cations in solution; half-life times of exchange are 855 (Na+) and 528 (Rb+) h in acetone and 352 (Na+) and 845 (Rb+) h in Me2SO, respect ively. The results of this method were verified by an independent H-1 NMR spectroscopic method.