Metallocomplex catalysis in oxidation processes. Kinetics and mechanisms.

Abstract

Ways of increasing catalytic activity of complexes of transition metals towards oxidation of alkylarenes with molecular oxygen, described in the literature within last 10-15 years, are reviewed. Attention is focused on the original method of controlling the catalytic activity of complexes of M(acac)n (M=Ni(II), Fe(II,III), Co(II)) in the oxidation reactions of alkylarene (e.g., ethylbenzene and cumol) to hydroperoxides by introducing the mono- or polydentate electron-donating ligands L2. Modeling of the catalytically active complexes of nickel as selective catalysts for ethylbenzene oxidation to α-phenylethylhydroperoxide by introducing phenol (PhOH) in the binary system {Ni(II)(acac)2+L2}, and also active complexes of nickel or iron by using quaternary ammonium salts and macrocyclic polyethers as L2, is successfully realized by the authors. The role of H-bonding in the mechanisms of the homogeneous catalysis is discussed. A strategy of controlling the catalytic activity of Fe(II,III)(acac)nL2 complexes (L2 =R4NBr or 18-crown-6 (18C6) by introducing small amounts of H2O (~10-3 mol/l) is proposed. The activity of Ni and Fe catalysts in the processes of radical chain initiation (O2 activation) and radical chain propagation (Catalyst + RO2 →) in the reactions of ethylbenzene oxidation is discussed. The bibliography includes 144 references.

Keywords

• homogeneous catalysis, oxidation, alkylarenes, hydroperoxides, molecular oxygen, ni(ii) - fe(ii,iii) acetylacetonates, hmpa, dmf, mst (m=na, li, k), quaternary ammonium salts, macrocyclic polyethers, phoh, low concentration of h2o (~10-3 mol/l).