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 s o-called 'Co(III) acetate'-reactive intermediate of cobalt acetate cat alyzed autoxidation, is the mixture of the oxo-centered trinuclear cat ions [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. Imme diately 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 o f p-xylene to the sample containing I and II under anaerobic condition s in CH,CI, (1:3 p-xylene/CH2Cl2 by volume, 293 K) gave rise to gradua l 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.