DIOXYGEN ADDUCTS OF COBALT(II) COMPLEXES OF 6,6'-BIS(P-SUBSTITUTED BENZOYLAMINO)-2,2'-BIPYRIDINES AND THEIR CATALYTIC ACTIVITIES IN OXYGENATION OF 2,6-DI-TERT-BUTYLPHENOL

The oxygen affinities and properties of oxygen adducts of complexes [CoL] [H-2L = 6,6'-bis(benzoyl-amino)-2,2'-bipyridine and its 4-methyl-, -tert-butyl or -chloro-benzoylamino analogues] has been studied by cyclic voltammetry and IR, electronic and ESR spectroscopy. The complexes exhibited oxygen-binding ability in the presence of an appropriate axial base ligand (B), and the oxygen adducts were of the end-on bonded Co(III) (O2) type [CoL(B)(O2)]. More complete electron transfer from the metal centre to the oxygen was indicated compared to that with [Co(salen)] [H-2salen = N,N'-ethylenebis(salicylideneimine)]. Electron-donating substituents gave higher concentrations of the oxygen adducts. The superior catalytic activity of these complexes, especially the Me- and Bu(t)-substituted derivatives, in the oxygenation of 2,6-di-tert-butylphenol to the corresponding quinone is interpreted in terms of the reactivity of the co-ordinated oxygen and the oxygen affinity of the complexes.