The circular dichroism
spectra are reported for tetraamminecobalt(III) complexes with the chiral amino
alcohols 2-aminopropan-1-ol, 2- aminobutan-1-ol, 1-aminopropan-2-ol,
2-amino-1-phenyl-ethanol, ψ- ephedrine and ephedrine with the alcohol
groups protonated (OH) and deprotonated (O-). The solvent dependence of the
chemical shifts of the NH protons was investigated to determine the effects of
stereoselective solvation on the circular dichroism, but, in contrast to some
other related systems, the chemical shift difference between the two NH2
protons was relatively insensitive to solvent. Consistent with this, the
circular dichroism spectra of the tetraphenylborate salts of the deprotonated
complexes were found not to be markedly dependent on solvent. Tetraammine-{(-)-ψ-ephedrine)cobalt(III)
and tetraammine{(-)- ephedrine}cobalt(III) were found to have the same signs of
Cotton effects for the various d-d transitions, whereas bis{(-)-ψ-
ephedrine}copper(II) and bis{(-)-ephedrine}copper(II) had opposite signs. This
has been explained in terms of different conformer populations in the
cobalt(III) and copper(II) systems.
Cover Picture: A Theoretical Study of the Mechanism of the Desymmetrization of Cyclic meso-Anhydrides by Chiral Amino Alcohols (ChemCatChem 9/2010)
