Metallophthalocyanine functionalized silicas: catalysts for the selective oxidation of aromatic compounds

Metallophthalocyanines of iron, manganese and cobalt have been successfully anchored onto the surface of mesoporous and amorphous silicas and used as catalysts in the liquid phase oxidation of 2-methylnaphthalene and 2,3,6-trimethylphenol with hydrogen peroxide and t-butylhydroperoxide. The iron tetrasulfophthalocyanine showed an activity from far superior to that. of the other metallic complexes and to the corresponding homogeneous catalysts. The activity and selectivity depend on the nature of the solvent, oxidizing agent and the catalyst itself. In particular, iron tetrasulfophthalocyanine anchored in the dimeric form yielded catalyst much more active and selective that those containing monomeric species, which was unexpected since dimeric species are usually considered as inactive in homogeneous systems. The catalytic properties of these materials were compared with those of Ti containing silica-based molecular sieves. The latter were active in the oxidation of 2,3,6-trimethylphenol but not in that of 2-methylnaphthalene. Iron (III) peroxo species, formed by reaction of the peroxide with iron phthalocyanine were proposed to undergo a homolytic or heterolytic cleavage of O-O bond in case of the monomeric and dimeric complexes, respectively, to explain the difference in their catalytic properties. (C) 2000 Elsevier Science B.V. All rights reserved.