A bio-inspired Fe(III) complex and its use in the cyclohexane oxidation Giselle C. Silva a , Gabrieli L. Parrilha b , Nake ´dia M.F. Carvalho a , Valderes Drago c , Christiane Fernandes b , Adolfo Horn Jr. b , O.A.C. Antunes a, * a Instituto de Quı ´mica, Universidade Federal do Rio de Janeiro, Cidade Universita ´ria CT Bloco A-641, Rio de Janeiro, 21941-909 RJ, Brazil b Laborato ´rio de Cie ˆncias Quı ´micas, Universidade Estadual do Norte Fluminense, Campos dos Goytacazes, 28013-600 RJ, Brazil c Departamento de Fı ´sica, Universidade Federal de Santa Catarina, Floriano ´polis, 88040-900 SC, Brazil Available online 22 January 2008 Abstract The use of monooxygenase biomimetic catalysts has demonstrated good efficiency in the hydrocarbon oxidation. In this work we have used the complex [Fe III (HBPClNOL)(Cl) 2 ]ÁH 2 O as catalyst in the cyclohexane oxidation and the products cyclohexanol, cyclohexanone and adipic acid were obtained. Cyclohexyl hydroperoxide and the tert-butyl cyclohexyl peroxide were also obtained as byproducts. The best reaction condition was reached with the system H 2 O 2 –acetonitrile at 50 8C, with 26.9% of yield. The investigation of the catalysis over time showed that the yields increase until 24 h, although the reaction rate is greater in the first 6 h. The electronic spectra of the complex were measured during the cyclohexane oxidation and it was possible to verify the disappearance of the bands assigned to the charge transfer from the phenolate and the chloride ligands to the iron. This indicates that electronic and/or structural changes are happening with the iron compound, confirming the existence of interaction between the complex and the oxidant. # 2007 Elsevier B.V. All rights reserved. Keywords: Selective cyclohexane oxidation; Cyclohexanol; Cyclohexanone; Cyclohexyl hydroperoxide; tert-Butyl cyclohexyl peroxide; Adipic acid; Iron(III) mononuclear complex; [Fe III (HBPClNOL)(Cl) 2 ]ÁH 2 O; Peroxides; Methane monooxygenase models 1. Introduction The hydrocarbon functionalization is an important object of study due to its abundance in nature. Among them, alkanes are characterized to be inert compounds in presence of most of the chemical reagents because of the high stability of their C–C and C–H bonds, making its transformation somewhat hard [1]. Direct methanol production would eliminate the use synthesis gas pathway, which is the method used by industry to obtain methanol [2]. Cheaper production of methanol would enable industrial conversion in dimethyl ether (DME), a substitute to diesel (C15) and bottled kitchen (butanes) gas substitute. Cyclohexane is another important hydrocarbon for industry due to the fact that its oxidation products cyclohexanol and cyclohexanone are adipic acid precursors. Adipic acid has a large industrial application in the Nylon-6 and Nylon-66 manufacture (production around million tons per year in the world), urethane foams, lubricant additives, production of pharmaceutical intermediates, insecticides and bactericides [3,4]. Cyclohexane derivatives industrial production involves a system that uses cobalt salts, molecular oxygen and tempera- tures above 150 8C, with conversions around 4% and selectivity of 85%. Due to the high energy used in this process, systems that are performed at mild condition are desirable [5–8]. Methane monooxygenase (MMO) biomimetic systems could be the best alternative of catalyst once this enzyme works at room temperature and atmospheric pressure. Mono- oxygenases are enzymes which catalyze the insertion of one oxygen atom from O 2 in a substrate molecule while the other oxygen atom is reduced to water [9,10]. MMO is a specific type of monooxygenase, isolated from the methanotrophic bacteria Methilococus capsulatus (bath) and Methilosinus tricosporium (OB3b), responsible for the methane conversion into methanol. The MMO mechanism involves the intermediate Q formation, which iron gets its highest oxidation state keeping a binuclear cluster Fe(IV) 2 connected by a m-oxo bridge, which is the main reactive species of the cycle [11–15]. The advantage of using the MMO analogous complexes is that besides oxidizing the methane, other types of hydrocarbon also may be oxidized such alkanes, alkenes, sulfites, aromatics, substituted aliphatic and www.elsevier.com/locate/cattod Available online at www.sciencedirect.com Catalysis Today 133–135 (2008) 684–688 * Corresponding author. Tel.: +55 21 2562-7818; fax: +55 21 2562-7559. E-mail address: octavio@iq.ufrj.br (O.A.C. Antunes). 0920-5861/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2007.12.036