The Stereochemistry and Reactivity of Metal-Schiff Base Complexes. III. The Kinetic and Thermodynamic Stereoselectivities in the Formation of N,N′-Ethylenebis(α-methylsalicylideneaminato)cobalt(III)Complexes with l-Proline, Hydroxy-l-proline, and allo-Hydroxy-l-proline
- 1 December 1980
- journal article
- research article
- Published by Oxford University Press (OUP) in Bulletin of the Chemical Society of Japan
- Vol. 53 (12) , 3537-3546
- https://doi.org/10.1246/bcsj.53.3537
Abstract
Under air-oxidation conditions, the reaction of [Co(α-Me-sal2en)] with L-aaH, where α-Me-sal2en represents the dianion of N,N′-ethylenebis(α-niethylsalicylideneaniine) and where L-aaH denotes L-proline, hydroxy-L-proline, or allo-hydroxy-L-proline, proceeded rapidly to yield Λ-cis-β2–[Co(α-Me-sal2en)(L-aa)] stereoselectively, followed by the slow isomerization of the Λ-cis-β2-isomer thus formed to give the corresponding Δ-cis-β2-isomer in a yield of almost 100% under equilibrium conditions. The complexes thus formed were isolated and characterized by the use of their absorption, circular dichroism, and 1H-NMR spectra. The preferential formation of the Λ-cis-β2-isomer in the initial reaction was found to be kinetic in origin. The kinetic stereoselectivity was determined to be 87% for L-proline, 56% for hydroxy-L-proline, and 23% for allo-hydroxy-L-proline by the measurement of the rotation at 435 nm of the reaction solutions. On the other hand, no kinetic differentiation was observed for the formation of the similar cis-β2-complexes with L-alanine, L-valine, L-methionine, L-phenylalanine, L-tryptophan, N-benzyl-L-alanine, and N-methyl-L-alanine. On the basis of these data, the mechanism of the initial complexation was discussed. The high thermodynamic stereoselectivity for Δ-cis-β2-isomer was explained in terms of the intramolecular steric interaction between the pyrrolidine ring of the coordinated L-aa and the distorted α-Me-sal2en ligand in the complex.Keywords
This publication has 20 references indexed in Scilit:
- Asymmetric transformation of .alpha.-amino acids promoted by optically active cobalt(III) complexesInorganic Chemistry, 1980
- Preparation and Characterization of uns-cis-Trimethylenediamine-N,N′-diacetato Cobalt(III) Complexes with Several l-Amino AcidsBulletin of the Chemical Society of Japan, 1979
- Amino acid mediated asymmetric transformation and catalytic asymmetric transformation of the .alpha.-triethylenetetraminecobalt(III) moietyJournal of the American Chemical Society, 1978
- Asymmetric transformation of α-amino acids promoted by optically active metal complexesPure and Applied Chemistry, 1978
- The Stereochemistry and Reactivity of Metal-Schiff Base Complexes. II. High Stereoselectivity in (1S,2S)-N,N′-1,2-Cyclohexylenebis-(salicylideneaminato)(sal2-(S,S)-chxn) Cobalt(III) Complexes with Amino Acids and the Optical Resolution of Amino Acids with Cobalt(III)-sal2-(S,S)-chxnBulletin of the Chemical Society of Japan, 1977
- Stereochemistry and Reactivity of Metal–Schiff-base Complexes. I. Preparation and Thermodynamic Stereoselectivity of Mixed Ligand Cobalt(III) Complexes Containing N,N′-Ethylenebis(salicylideneamine) Dianion (sal2en) or N,N′-Ethylenebis(7-methylsalicylideneamine) Dianion (7,7′-Me-sal2en) and l-Amino Acid AnionBulletin of the Chemical Society of Japan, 1976
- Stereoselectivities in Mixed Ligand Complexes of Cobalt(III), with l-Asparagine as a LigandBulletin of the Chemical Society of Japan, 1976
- Absence of selectivity in the synthesis and equilibration of [Co(en)2(S-glu)]+ IonsInorganic Chemistry, 1973
- Model complexes of products expected from N-terminal hydrolysis of polypeptides containing trifunctional amino acids. Tetraminecobalt(III) complexes of glutamic and aspartic acidsInorganic Chemistry, 1971
- Prediction of molecular geometries and relative stabilities in chelate complexes. Application of cobalt(III) triethylenetetramine-(S)-prolinato complexesJournal of the American Chemical Society, 1970