Preparation and Stereochemistry of Δ-sym-cobalt(III) Complexes with Various Bidentate Ligands

Article abstract of DOI:10.1246/bcsj.56.157

Cobalt(III) complexes containing (2S,2'S)-1,1'-ethylenedipyrrolidine-2,2'-dicarboxylate (S,S-epro) and a bidentate ligand were prepared and characterized.The bidentate ligands were ethylenediamine, trimethylenediamine, oxalate, glycinate, (R)- or (S)-alaninate, (R)- or (S)-valinate, (R)- or (S)-prolinate, (R)- or (S)-pipecolate, sarcosinate, or N-ethylglycinate.The S,S-epro ligand coordinates stereoselectively to cobalt(III) ion to take only the Δ-sym configuration.The stereochemistry was discussed on the basis of the electronic absorption, CD, and 1H and 13C NMR spectra.The rate constants of isomerization and the Gibbs' free energy difference (ca. 0.9 kJ mol^-1) between the R(N) and S(N) isomers of the sarcosinato or N-ethylglycinato complex were investigated in relation to the interligand interaction.The thermodynamics and mechanisms of their isomerization process were little influenced by the N-alkyl groups.