Synthesis, characterization, and catalytic activity of anionic iron(III) porphyrins intercalated into layered double hydroxides

The first generation free-base anionic porphyrin [H2(TSPP)]4−, its iron(III) porphyrin [Fe(TSPP)]3−, and the second generation anionic complexes [Fe(TDFSPP)]3− and [Fe(TDCSPP)]3− were intercalated into the layered double hydroxide ZnnAl-LDH (image, 4 or 5) by coprecipitation at constant pH. The materials were characterized by X-ray powder diffraction, UV/visible spectroscopy in glycerin mull, attenuated total reflectance Fourier transform infrared spectroscopy, and electron paramagnetic resonance. Results revealed that the coprecipitation method led to intercalation of the free-base porphyrin and the iron(III) porphyrins between the ZnnAl-LDH layers. The materials were used as catalysts in the oxidation of cyclooctene, cyclohexene, and cyclohexane by iodosylbenzene. The catalytic activity of [Fe(TDCSPP)]-Zn2Al-LDH was higher than that of the homogeneous [Fe(TDCSPP)]3−, but the opposite effect was observed in the case of [Fe(TDFSPP)]-Zn2Al-LDH. Although [Fe(TDFSPP)]3− and [Fe(TDCSPP)]3− are structurally similar, their intercalation into Zn2Al-LDH likely results in different chemical environments, leading to distinct catalytic activities.