Immobilization of anionic metalloporphyrins on zinc hydroxide nitrate and study of an unusual catalytic activity

This paper is the first report on the immobilization of an anionic iron(III) porphyrin family on zinc hydroxide nitrate (ZHN), a layered hydroxide salt. ZNH was prepared by means of a precipitation reaction between a zinc nitrate solution and ammonium hydroxide. Two immobilization systems were investigated, namely magnetic stirring at room temperature and stirring/reflux in an ethanolic solution. The solids were characterized by powder X-ray diffraction (XRD), electron paramagnetic resonance (EPR), thermogravimetric and derivative thermogravimetric (TGA/DTG), transmission electron microscopy (TEM), as well as ultraviolet–visible (UV–Vis) and Fourier transform infrared (FTIR) spectroscopic analyses. The catalytic activity of the materials was investigated in the oxidation of cyclooctene, cyclohexane, and n-heptane using iodosylbenzene as oxygen donor. The oxidation products were analyzed by gas chromatography. The results revealed an unusual selectivity for cyclohexanone in the reactions of cyclohexane oxidation catalyzed by the anionic iron(III) porphyrins immobilized onto ZHN. These results suggest that the structure of the ZHN support influences the catalytic mechanism and that cyclohexane oxidation occurs via a radicalar pathway.