Light-assisted cyclohexane oxidation catalysis by a manganese(III) porphyrin immobilized onto zinc hydroxide salt and zinc oxide obtained by zinc hydroxide salt hydrothermal decomposition

Abstract Two manganese(III) porphyrin complexes prepared with the tetra anionic free base porphyrin (Na4[H2(TDFSPP)]) and two different manganese(II) salts (manganese(II) acetate - MnP(OAc) complex and manganese(II) chloride - MnP(Cl) complex) were immobilized onto zinc hydroxide nitrate (ZHN), a layered hydroxide salt, and also into zinc oxide (ZnO), obtained via hydrothermal decomposition of the ZHN. The resulting solids, MnP(OAc)-ZHN, MnP(Cl)-ZHN, MnP(OAc)-ZnO and MnP(Cl)-ZnO, were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), electronic paramagnetic resonance (EPR) and ultraviolet-visible spectroscopy (UV-Vis) (solid samples). Manganese and consequently the immobilized manganese porphyrin complexes were quantified by ICP OES. The materials were applied as catalysts for the oxidation of cyclohexane, using iodosylbenzene as the oxygen donor, under conventional conditions (absence of light) as well as using light assisted conditions. Good catalytic results were obtained and, in absence of light, an unusual selectivity for the ketone was observed when using MnP(OAc)-ZHN as catalyst different from what can be observed when the catalyst is the solid MnP(Cl)-ZHN, that present selectivity to alcohol, suggesting an influence of both axial ligand and support in the catalytic activity.