Preparation and Stereochemistry of Cobalt(III) Complexes Containing 2,2′-Bipyridine 1,1′-Dioxide

Abstract

Abstract New cobalt(III) complexes, [Co(N4)(bpdo)]3+ (N4 = (en)2, (tn)2, (NH3)4, and tren; bpdo = 2,2′-bipyridine 1,1′-dioxide) and [Co(en)2(rac-3,3′-Me2bpdo)]3+ (rac-3,3′-Me2bpdo = racemic3,3′-dimethyl-2,2′-bipyridine 1,1′-dioxide), were obtained, where tn and tren denote trimethylenediamine and 2,2′,2″-triaminotriethylamine, respectively. The [Co(en or tn)2(bpdo)]3+ and [Co(en)2(rac-3,3′-Me2bpdo)]3+ complexes form only one of two possible racemic pairs of diastereomers, which were resolved by SP-Sephadex column chromatography. Each pair of these complexes was assigned to have a lel(Δ(λ), Λ(δ)) structure on the basis of the 13C NMR and circular dichroism spectra, and the absolute configuration of optically active free 3,3′-Me2bpdo ligand recovered from the resolved complex. The tetraammine and tren complexes were resolved into a pair of enantiomers by a chemical method, but rapidly racemized in water with the rate of 7.33 × 10−3 s−1 and 1.16 × 10−3 s−1, respectively, at 10.0 °C. An intramolecular conformational inversion of the skew bpdo chelate ring (δ λ) was proposed for the racemization.