Preparation and Stereochemistry of Optical Isomers of the Tris-(3,3′-dimethyl-2,2′-bipyridyl <i>N</i>,<i>N</i>′-dioxide)chromium(III) Complex

Abstract

Abstract A new ligand, (R)- and (S)-3,3′-dimethyl-2,2′-bipyridyl N,N-dioxide(mbdo) forms three diastereomers(I, II, and III) of [Cr(mbdo)3]3+ by the reaction with [Cr(H2O)6]3+ in water. (I) was assigned to a pair of enantiomers, Δ(RRR) and Λ(SSS), and (II) and (III) to either a diastereomeric pair of Δ(RRS) and Λ(SSR) or Δ(SSR) and Λ(RRS). While the racemic (I) was resolved by SP-Sephadex column chromatography, (II) and (III) isomerized in water to each other (II\ightleftarrowsIII) by exposure to ultraviolet light, were resolved by the reaction of [Cr(H2O)4(R or S)-mbdo]3+ with a stoichiometric amount of (S or R)-mbdo. The circular dichroism spectra of these optically active isomers were measured in aqueous solutions and compared with those of complexes of the [CrO6]-type of known absolute configuration. The optically active free (+)589- and (−)589-mbdo were isolated by decomposing Λ(SSS)- and Λ(RRR)-[Cr(mbdo)3]3+, respectively, with edta4−. The active mbdo is optically stable even in boiling water.