Immobilization of b halogenated ironporphyrin in the silica matrix by the sol–gel process Ednalva Aparecida Vidoto a , Maria Silvia Monsalves Moreira a , F abio da Silva Vinhado a , Katia Jorge Ciuffi b , Otaciro Rangel Nascimento c , Yassuko Iamamoto a, * a Departamento de Qu  ımica, FFCLRP, Universidade de S~ ao Paulo, Av. Bandeirantes, 3900, CEP 14040-901, Ribeir ~ ao Preto, SP, Brazil b Universidade de Franca, 14404-600 Franca, SP, Brazil c Universidade de S~ ao Paulo, 13560-250 S~ ao Carlos, SP, Brazil Abstract We present the synthesis and characterization of a hybrid organic–inorganic material using robust metallopor- phyrins halogenated in both meso and b-position: the iron complex (5,10,15,20-tetrakis-(pentafluorophenyl) porphyrin and (2,3,7,8,12,13,17,18-octa-b-bromo-5,10,15,20-tetrakis-(pentafluorophenyl) porphyrin, which stabilize the por- phyrins against oxidative degradation. The immobilization was developed by the sol–gel process using pyridine and imidazole as template. Electron paramagnetic resonance (EPR) spectra of (2,3,7,8,12,13,17,18-octa-b-bromo- 5,10,15,20-tetrakis-(pentafluorophenyl) porphyrin show that the entrapment of ironporphyrin is in a higher symmetry compared to the systems in solution. A reduction of iron was observed in the presence of imidazole, determined by the absence of an EPR spectrum. The addition of chloridric acid vapor induced an oxidation of iron and a small quantity of iron in a high spin state was detected by a component with axial symmetry. The ironporphyrins were active as catalysts for cyclooctene using iodozylbenzene and hydrogen peroxide as oxygen donors. The perhalogenated porphyrins im- mobilized had a smaller activity due to their iron oxidation and spin states. Ó 2002 Elsevier Science B.V. All rights reserved. 1. Introduction Metalloporphyrins are important prosthetic groups in a number of biological molecules and enzymes [1]. They have been used as catalyst in oxidation reactions, mimicking cytochrome P-450 [2–6]. The most efficient systems involve ironpor- phyrins bearing electron-withdrawing substituents on the aryl group. The improved catalytic effi- ciency of metalloporphyrins due to the presence of halogen atoms attached to the tetrapyrrolic mac- rocycle prompted much research on the synthesis of the b-substituted porphyrins. The resultant b- octahalogenated metalloporphyrins have been re- ported to be much more active and significantly more stable than that b-unsubstituted analogous [7–10]. A problem associated with hydrocarbon oxidation catalyzed by metalloporphyrins is the Journal of Non-Crystalline Solids 304 (2002) 151–159 www.elsevier.com/locate/jnoncrysol * Corresponding author. Tel.: +55-16 602 3782; fax: +55-16 633 8151. E-mail address: iamamoto@usp.br (Y. Iamamoto). 0022-3093/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0022-3093(02)01019-0