Circular dichroism studies for absolute configuration determination of 1,2-diaminopropane chromium(III) complexes, and synthesis of tetracyano(1,2-diaminopropane)chromate(III)

Abstract

This is the first study of the absolute configuration determinations for metal complexes coordinated by chiral propylenediamine ligands, using CD spectra. The CD (circular dichroism) spectra of analogous Cr(III) complexes represented by [Cr(CN) 2 n ,(A) 3− n ] 3−2 n (A=pn or en, n=0 or 1, pn= d-pn orℓ-pn and pn=1,2-diaminopropane=propylenediamine, en=ethylenediamine) have been systematically measured, and they have been compared with that of the Λ- cis-(-) 589-[Cr(CN) 2( d-pn) 2]Cl standard, of which an absolute configuration has been confirmed by X-ray analysis, and absolute configurations of the seven complexes have been collectively determined. In this study the two new complexes of tetracyano( d- or ℓ-1,2-diaminopropane)chromate(III) are synthesized to learn the contribution of the chiral configurations, localized upon the propylenediamine ligands, to CD spectra of complexes, because CD peaks, depending on the chiral propylenediamine, are liable to interfere with correct absolute configuration determinations. We have elucidated the effectiveness of using CD spectra as the absolute configuration determination method. The superiority of this method is particularly obvious when complexes cannot answer to X-ray analysis-as was the case with several complexes in this study-due to the difficulty in preparing single crystals.