The Stereochemistry and Reactivity of Metal–Schiff Base Complexes. V. The Solvent Effect on the Stereoselectivity of Cobalt(III) Complexes Containing a sal2en-type Schiff Base and l-Amino Acid
- 1 August 1982
- journal article
- research article
- Published by Oxford University Press (OUP) in Bulletin of the Chemical Society of Japan
- Vol. 55 (8) , 2598-2610
- https://doi.org/10.1246/bcsj.55.2598
Abstract
The solvent effect on the stereoselectivity between Λ- and Δ-β2-diastereoisomers of cobalt(III) complexes with the general formula of [Co(Schiff base)(L-aa)], where Schiff base represents sal2en2−, α-Me-sal2en2−, and 5,6-benzo-sal2en2−, and where L-aa denotes L-alaninate, L-valinate, L-methioninate, and L-phenylalaninate, was studied. Generally, the Λ-β2-isomer was more stable than the Δ-β2-isomer in solution, and the stereoselectivity of all the L-ala-complexes and of the L-met-complex with 5,6-benzo-sal2en increased in the following order of solvents : acetone=DMF≤t-BuOH<s-BuOH<i-PrOH<n-BuOH<n-PrOH2en and 5,6-benzo-sal2en increased in the following order : acetone=DMFn-PrOH<n-BuOH<i-PrOH<s-BuOH<t-BuOH. In the case of 5,6-benzo-sal2en complexes with L-val and L-ile, the Δ-β2-isomer was preferred rather than the Λ-β2-isomer in acetone and DMF with 8–13% stereoselectivity. From the spectroscopic evidence, a hydrogen bonding between the OH group of alcoholic solvents and phenolic oxygen atoms of a Schiff base ligand was assummed, and the above phenomena were explained in terms of the steric difference between the Λ- and Δ-β2-isomers for the solvation with the alcoholic solvents by means of the hydrogen bonding.Keywords
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