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 ' -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, delta reversible arrow lambda. The rate of racemization is remarkably reduced with an increase in the electron-releasing ability of the 4,4 ' -X-2 substituents on bpdo. (C) 2001 Elsevier Science B.V. All rights reserved.