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

A new series of cobalt(III) complexes, [Co(2,2′,2′′-triaminotriethylamine)(4,4′-X2bpdo)]3+ (X=Me, MeO, EtO), where 4,4′-X2bpdo 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′-X2bpdo chelate ring, δ⇌λ. The rate of racemization is remarkably reduced with an increase in the electron-releasing ability of the 4,4′-X2 substituents on bpdo.