Multinuclear NMR spectroscopic characterization of Co(III) species: Key intermediates of cobalt catalyzed autoxidation

Using H-1, C-13 and Co-59 NMR spectroscopies, it was shown that, the so-called 'Co(III) acetate'-reactive intermediate of cobalt acetate catalyzed autoxidation, is the mixture of the oxo-centered trinuclear cations [Co3O(OAc)(6)(AcOH)(3)](+) (I) and [Co3O(OAc)(5)(OH)(AcOH)(3)](+) (II) in 1:3-1:2 ratio. Cations I and II are the major species in the freshly prepared solutions of Co(III) acetate in CH2Cl2 and AcOH. Immediately after dissolving in MeOH, I converts into cation [Co3O(OAc)(5)(OMe)(MeOH)(3)](+) and II into cation [Co3O(OAc)(5)(OH)(MeOH)(3)](+). Reactivity of I and II towards p-xylene was determined. The addition of p-xylene to the sample containing I and II under anaerobic conditions in CH,CI, (1:3 p-xylene/CH2Cl2 by volume, 293 K) gave rise to gradual decrease of their concentration. The half-life was 2 h for cation II and 1.3 h for cation I. (C) 1998 Elsevier Science B.V.