Diastereomeric discrimination in 1,4,7-tris((S)-2-hydroxypropyl)-1,4,7-triazacyclononane and its lithium(I), sodium(I) and zinc(II) complexes

In methanol, interchange between equivalent forms of a single diastereomer of 1,4,7-tris((S)-2-hydroxypropyl)-1,4,7-triazacyclononanelithium(I), [Li(S -thpc9)](+), and a similar interchange in [Na(S-thpc9)](+) have been charac terised by variable temperature C-13{H-1} NMR spectroscopy. The respective kinetic parameters are: k=33.5 +/-0.8 and 3030 +/- 80 s(-1) at 298.2 K, Del taH double dagger =50.6 +/-1.0 and 50.9 +/-1.3 kJ mol(-1), and DeltaS doubl e dagger=-46.1 +/-3.4 and -7.6 +/-4.7 J K-1 mol(-1), with the corresponding log(K/dm(3) mol(-1))=3.39 +/-0.05 and 2.50 +/-0.05 at 298.2 K and I=0.05 m ol dm(-3) (NEt4ClO4), where K is the complex stability constant. In N,N-dim ethylformamide (DMF), log(K/dm(3) mol(-1))= 3.29, 2.29, 2.28, 2.27, 2.29 an d 7.59 (all +/-0.05) for [M(S-thpc9)](+) where M+=Li+, Na+, K+, Rb+, Cs+ an d Ag+, respectively. For the interchange between equivalent forms of a sing le diastereomer of 1,4,7-tris((S)-2-hydroxy-2-phenylethyl)-1,4,7-triazacycl ononanelithium(I), [Li(S-thpec9)](+), and a similar interchange in [Na(S-th pec9)](+), the kinetic parameters obtained in DMF are: k=20.5 +/-0.8 and k= 8600 +/- 200 s(-1) at 298.2 K, DeltaH double dagger =32.8 +/-1.8 and 54.7 /-1.2 kJ mol(-1), and DeltaS double dagger=-110 +/-3.2 and 13.8 +/-4.2 J K- 1 mol(-1), respectively. In DMF, log(K/dm(3) mol(-1))=3.64, 2.03, 1.91, 1.9 1, 1.62 and 7.59 (all +/-0.05) for [M(S-thpc9)](+) where M+=Li+, Na+, K+, R b+, Cs+ and Ag+, respectively. Gas phase ab initio modelling shows S-thpc9, S-thpec9 and their Li+, Na+ and Zn(II) complexes to assume single distorte d trigonal prismatic diastereomeric conformations, as do X-ray crystallogra phic, ab initio modelling and C-13{H-1} NMR spectroscopic solution studies of [Zn(S-thpc9)](+).