Stereoselectivity in the series of bis[N-salicylidenaminoacidato]cobaltate(III) ions as a function of properties of the solvent and bulk of substituents in the salicylaldehyde nucleus

Abstract

1. Three complexes of sodium bis[N-3-substituted-salicylidene-S-valinato]cobaltate(III) were synthesized where the salicylaldehyde residue was substituted in position 3 with the NO2, i-C3H7, and t-C4H9 groups. The Λ (SS)- and Δ (SS)-diastereomers of the complexes were separated and their structure and configuration were demonstrated by elemental analysis and physical methods. 2. The stereoselective effects in these compounds were studied and it was shown that by varying the bulk and electronic effects of groups in the salicylaldehyde ring (from 5-NO2 to 3-t-C4H9) the relative energy of diastereomers can be changed in the interval of 2.6 kcal/mole. 3. Stereoselective effects were studied in the complexes potassium Λ- and Δ-bis[N-salicyliden-S-alaninato ]cobaltate(III) and potassium Λ- and Δ-bis[N-salicylidene-S-valinato]cobaltate(III) in various solvents and it was shown that the solvent has at least no less an effect on the energy difference of diastereomers than do the substituants introduced into the complex molecule. 4. The energy difference of diastereomers in a series of alcohols correlates with the dielectric constant of the solvent, which indicates the important role of electrostatic interactions in complexes.