The Stereochemistry and Reactivity of Metal-Schiff Base Complexes. IV. The Stereoselectivity of N,N′-Ethylenebis(α-methylsalicylideneaminato)cobalt(III) Complexes with N-Benzyl-l-alanine, N-Methyl-l-alanine, and N-Benzyl-N-Methyl-l-alanine, and the Stereospecificity of [1S, 2S)-N,N′-1,2-Cyclohexylenebis(salicylideneaminato)cobalt(III) Complexes toward N-Benzyl-l-alanine

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Abstract
Cobalt(III) complexes containing N-alkyl-L-alanine and a Schiff base ligand, β2-[Co(α-Me-sal2en)(N-R-L-ala)] (where α-Me-sal2en represents the dianion of N,N′-ethylenebis(a-methylsalicylideneamine) and N-R-L-ala denotes the anion of titled amino acids), have been prepared. They were characterized by the use of the absorption, circular dichroism, and 1H NMR spectra of the complexes. They showed quite high stereoselectivity for ΛRS-β2-configuration: 93% for N-methyl-L-alanine, and almost 100% for N-benzyl-L-alanine and N-benzyl-N-methyl-L-alanine. The similar β2-Co(sal2-(S,S-chxn) complexes with N-benzyl-L- and N-benzyl-D-alanines, where sal2-(S,S)-chxn represents the dianion of (1S,2S)-N,N′-1,2-cyclohexylenebis(salicylideneamine), have been synthesized to investigate the stereospecificity of the complex toward N-benzyl-L-alanine. It was found that Co(sal2-(S,S)-chxn) complex reacts with N-benzyl-L-alanine in a high stereospecificity (93–94% at the 1 : 2 reaction molar ratio between the complex and racemic N-benzylalanine, and almost 100% at the 1 : 100 molar ratio). The above phenomena were explained in terms of the thermodynamic selectivity of the complexes.

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