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-tr imethylphenol with hydrogen peroxide and t-butylhydroperoxide. The iron tet rasulfophthalocyanine showed an activity from far superior to that. of the other metallic complexes and to the corresponding homogeneous catalysts. Th e activity and selectivity depend on the nature of the solvent, oxidizing a gent and the catalyst itself. In particular, iron tetrasulfophthalocyanine anchored in the dimeric form yielded catalyst much more active and selectiv e that those containing monomeric species, which was unexpected since dimer ic species are usually considered as inactive in homogeneous systems. The c atalytic properties of these materials were compared with those of Ti conta ining silica-based molecular sieves. The latter were active in the oxidatio n of 2,3,6-trimethylphenol but not in that of 2-methylnaphthalene. Iron (II I) peroxo species, formed by reaction of the peroxide with iron phthalocyan ine were proposed to undergo a homolytic or heterolytic cleavage of O-O bon d 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.