Conformation, of coordinated chelates

Diastereoisomerism is observed when two or more chiral elements appear in the same system. Isolation and characterization of enantiomers or diastereoisomers depend on the structural stability of the chiral element. Therefore the conformation of a chelate ring must generally be considered as labile. The structural stability of the configuration around the metal center and the stability of an asymmetric coordination atom depends on the nature of the central metal atom. In most cases an optically active ligand molecule can be considered as configurationally stable. The presence of a stable chiral element can induce definite chirality in another element which, taken separately, would be labile. 

Fig- 22. Conformation of the chelate rings in the crystal structure of (-)589-(/e/2oh)-[Co(chxn)3]Cl3 5 H2O. Numbers attached to each carbon atom indicate the distances from the coordination plane (Ref. 38)... 

The Si-F distance in 8 corresponds well with bond lengths found in other hypervalent silicon compounds (1.60-1.73 A) [Id, 6]. The distances Si-O and Si N are remarkably short [6]. The distortion of the octahedral coordination environment around silicon probably originates from the conformation of the chelating salen ligand. 

Nitrogen J couplings are peculiarly valuable in structure determination because of their sensitivity to the presence and orientation of a lone pair on the nitrogen. Thus they are usually diagnostic of coordination, chelation, protonation, or hydrogen bonding of the nitrogen, and reflect departures from planarity, conformational relationships, syn-anti or cis-trans stereochemistry, solvent effects and solution equilibria, and so on. 

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