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Stereoselectivity in reactions of metal-complexes. 15. Structure and stability of chiral cobalt(III) complexes with pentadentate ligands
Helvetica Chimica Acta
The syntheses and characterization of four new linear pentadentate ligands and their Co(III) complexes are described: N,N'-[(pyridine-2,6-diyl)bis(methylene)]bis[sarcosine] (sarmp), N,N'-[(pyridine-2,6-diyl)bis(methylene)]bis[(R)- or (SS)-promp), N,N'-[(pyridine-2,6-diyl)bis(methylene)]bis[N-(methyl)-(R)- or (S)-alanine] ((R,R)- or (S,S)-malmp); 2,2'-[pyridine-2,6-diyl]bis[(S)- or rac-N-(acetic acid)pyrrolidine] ((S,S)- or rac-bapap). The complexes were characterized and, with but one exception, complex formation is stereospecific: DELTA-exo-(R,R) (or LAMBDA-exo-(S,S)) for promp and LAMBDA-(R,R) (or DELTA-(S,S)) for bapap. The exception is [Co((R,R)- or (SS)-malmp)H2O]ClO4 for which two forms are obtained, to which LAMBDA-endo-(R,R) (or DELTA-endo-(S,S)) and, tentatively, DELTA-unsymmetric-(R,R)- (or LAMBDA-unsymmetric-(SS)-) configurations are assigned. X-Ray crystal structures are presented for the complexes [Co(sarmp)H2O]ClO4, [Co((S,S)-promp)H2O]ClO4, [Co(rac-bapap)H2O]ClO4 and endo-[Co(rac-malmp)H2O]ClO4. Ligand acid dissociation and Co(II) and Fe(II) complex-formation constants are reported.
Web of science
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