Hideaki Kanno

Conformational inversion of 2,2′-bipyridine 1,1′-dioxide chelate ring in a series of (2,2′,2′′-triaminotriethylamine)(4,4′-disubstituted-2,2′-bipyridine 1,1′-dioxide)cobalt(III) complexes

Abstract A new series of cobalt(III) complexes, [Co(2,2′,2′′-triaminotriethylamine)(4,4′-X 2 bpdo)] 3+ (X=Me, MeO, EtO), where 4,4′-X 2 bpdo denotes 4,4′-disubstituted-2,2′-bipyridine 1,1′-dioxide, were prepared. The complexes were resolved into a pair of enantiomers (conformational optical isomers), and gradually racemized in water by conformational inversion of the skewed 4,4′-X 2 bpdo chelate ring, δ⇌λ. The rate of racemization is remarkably reduced with an increase in the electron-releasing ability of the 4,4′-X 2 substituents on bpdo.

Isomerization and racemization of (acetylacetonato)bis(4,4′-dimethyl-2,2′-bipyridine 1,1′-dioxide)chromium(III), (acetylacetonato)bis(4,4′-dimethoxy-2,2′-bipyridine 1,1′-dioxide)chromium(III) and (acetylacetonato)bis(4,4′-diethoxy-2,2′-bipyridine 1,1′-dioxide)chromium(III) complexes

Abstract A series of chromium(III) complexes, [Cr(acetylacetonato)(4,4′-X 2 bpdo) 2 ] 2− (X = Me, MeO, EtO), where 4,4′-X 2 bpdo denotes 4,4′-substituted 2,2′-bipyridine 1,1′-dioxide, were prepared and resolved into pairs of enantiomers. The perchlorates of these complexes were found to crystallize in a lel 2 ( Δ ( λλ ), Λ ( δδ )) form; they isomerize to a lelob ( Δ ( λδ ), Λ ( δλ )) form in water, accompanied by rapid changes in the absorption spectra, and then racemize slowly. The rates of both isomerization and racemization are reduced with an increase in the electron-releasing ability of the 4,4′-X 2 substituent.