The reaction of a
cis ![](/images/gifchars/beta2.gif)
folded organocobalt derivative with a salen-type ligand,
1, isolated as racemic compoundof
![](/images/gifchars/Delta.gif)
and
![](/images/entities/Lgr.gif)
enantiomers, with enantiomerically pure
![](/images/gifchars/alpha.gif)
-
L amino acids is reported. The reaction between racemic
1 and
L-tyrosine afforded a mixture of the two diastereoisomers
![](/images/gifchars/Delta.gif)
-
2 and
![](/images/entities/Lgr.gif)
-
2, which could be separated by fractionalcrystallization owing to the lower solubility of
![](/images/gifchars/Delta.gif)
-
2. The absolute configuration of the two diastereomers wasunequivocally assigned from the X-ray structure, using the known absolute configuration of the asymmetric carbonof the amino acid as internal reference. The reaction of racemic
1 with
trans-4-hydroxy-
L-proline afforded only thediastereoisomer with a
![](/images/gifchars/Delta.gif)
configuration of the tetradentate ligand, as proved by X-ray diffractometric analysis. Forboth
L-tyrosine and
trans-4-hydroxy-
L-proline, the amino acid initially coordinates both to the
![](/images/gifchars/Delta.gif)
and to the
![](/images/entities/Lgr.gif)
enantiomers of
1, leading to an about equimolar mixture of diastereoisomers. In the case of
L-tyrosine thediastereoisomers have about the same energy, so that the successive isomerization is negligible. In the case of
trans-4-hydroxy-
L-proline,
![](/images/gifchars/Delta.gif)
-
3 is much more stable than
![](/images/entities/Lgr.gif)
-
3, and the isomerization reaction
![](/images/entities/Lgr.gif)
-
3
![](/images/gifchars/Delta.gif)
-
3 goespractically to completion.