Properties of (μ-oxo)di-iron complexes and catalytic activity toward cyclohexane oxidation

Abstract

We report herein the synthesis and characterization of two dinuclear m-oxo iron compounds obtained through the reactions of FeSO4•7H 2O and FeCl3•6H2O with 1-(bis-pyridin-2-ylmethyl-amino)-3-chloropropan-2-ol (L5), which resulted in the compounds [(SO4)(L5)Fe(μ-O)Fe(L5) (SO4)]•6H 2O, 1, and [Cl(L5)Fe(μ-O)Fe(L5)Cl]Cl2•2H 2O, 2. The electronic spectra of both compounds show absorption bands only in the UV range. The electrochemical analysis showed that the dinuclear unit is more stable under reduction in compound 1 than in compound 2, while the Mössbauer spectroscopy revealed that the monodentate ligands (sulfate and chloride) have a significant influence on the Mössbauer parameters determined for 1 and 2, particularly on the quadrupole splitting values. Both compounds were studied as catalysts in reactions of cyclohexane oxidation, using H2O2 and t-BuOOH as oxidants, in a substrate:oxidant: catalyst ratio of 1000:1000:1. Cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide, t-butyl cyclohexyl peroxide and adipic acid were formed during the process. The experiments revealed that compound 2 is, in general, more active than compound 1 in promoting cyclohexane oxidation. © 2010 Sociedade Brasileira de Química.