Alkali metal complexes of the pendant arm macrocyclic ligand 1,4,7,10-tetrakis(2-methoxyethyl)-1,4,7,10-tetraazacyclododecane. An equilibrium and inter- and intramolecular exchange study

The stability constant, K, of the alkali metal complexes of 1,4,7,10-tetrakis(2-methoxyethyl)-1,4,7,10-tetraazacyclododecane, [M(tmec12)](+), varies as M(+) changes in the sequence Li+ (9.34 +/- 0.05, 4.1 +/- 0.1, and 3.61 +/- 0.05), Na+ (9.13 +/- 0.05, 6.2 +/- 0.1, and 5.68 +/- 0.05), K+ (6.07 +/- 0.05, 3.9 +/- 0.1, and 3.62 +/- 0.05), Rb+ (4.85 +/- 0.05, 3.0 +/- 0.1, and 2.73 +/- 0.05), Cs+ (3.55 +/- 0.05, 2.5 +/- 0.1, and 2.28 +/- 0.05), and Ag+ (12.30 +/- 0.05, 14.2 +/- 0.1, and 13.73 +/- 0.05), where the figures in parentheses are log(K/dm(3) mol(-1)) in acetonitrile, methanol, and dimethylformamide, respectively, determined by potentiometric titration at 298.2 K and I = 0.05 mol dm(-1) (NE(4)ClO(4)). Analogous data are obtained in propylene carbonate and dimethyl sulfoxide. For monomolecular [Li(tmec12)](+) and [Na(tmec12)](+) decomplexation in dimethylformamide k(d)(298.2 K) = 31.4 +/- 0.4 and 7.6 +/- 0.3 s(-1), Delta H-d(double dagger) = 54.3 +/- 0.5 and 76.2 +/- 0.1 kJ mol(-1), and Delta S-d(double dagger) = -34.3 +/- 1.5 and 27.7 +/- 1.7 J K-1 mol(-1), respectively, determined by Li-7 and Na-23 NMR spectroscopy, and analogous data are reported for methanol and dimethyl sulfoxide solutions. The enantiomerization of Delta and Lambda square antiprismatic [Li(tmec12)](+) and their Na+ and K+ analogues in methanol, for which k(e)(298.2 K) = 32800 +/- 2400, 1470 +/- 100, and 415 +/- 4 s(-1), Delta H-e(double dagger) = 41.4 +/- 0.5, 31.4 +/- 0.9, and 50.7 +/- 0.2 kJ mol(-1) and Delta S-e(double dagger) = -19.7 +/- 2.6, -78.8 +/- 3.5, and -24.7 +/- 0.7 J K-1 mol(-1), respectively, occurs much more rapidly than intermolecular tmec12 exchange on these complexes.