Multinuclear NMR Spectroscopic Characterization of Co(III) Species: Key Intermediates of Cobalt Catalyzed Autoxidation
Journal of Molecular Catalysis A: Chemical
||59Co NMR spectroscopy, Catalytic oxidation, Co(III) acetate
Department of Natural Sciences, Novosibirsk State University, Novosibirsk 630090, Russia
Boreskov Institute of Catalysis, Pr. Akademika Lavrentieva 5, Novosibirsk 630090, Russia
Using Full-size image (<1 K), Full-size image (<1 K) and Full-size image (<1 K) 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 CH2Cl2 (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.