Synthesis and spectroscopic, electrochemical, and catalytic properties of a new manganese porphyrin bearing four positive charges close to the metal

A new Mn-porphyrin bearing four pyridinium substituents bound through their nitrogen atoms on the meso-positions of the tetrapyrrole ring was synthesized in three steps from Zn-β-octaethylporphyrin. It was characterized by elemental analysis, electrospray mass spectrometry, UV–vis and dual polarization mode EPR spectroscopy, and electrochemistry. Electrochemical and EPR studies showed that the Mn-porphyrin prepared by this method existed as a 80/20 Mn(II)/Mn(III) mixture, the redox potential of the Mn(III)/Mn(II) couple being +345 mV (versus SCE, in CH3CN). It catalyzed alkene epoxidation and alkane hydroxylation by PhIO with characteristics comparable to those of Mn[TDCPP = meso-tetra-(2,6-dichlorophenyl)porphyrin]Cl. It also catalyzed the hydroxylation of anisole, naphthalene and ethylbenzene by H2O2 in CH2Cl2/CH3CN, as well as the hydroxylation of the drug diclofenac by oxone in water. It is a new biomimetic catalyst exhibiting two distinctive characteristics: a good solubility in both hydrophobic aprotic solvents and water for pH > 5, and an unusual structure with four positive charges very close to the metallic centre.

Graphical abstractA new Mn-porphyrin, Mn(OEPy4P), was synthesized in three steps from Zn-β-octaethylporphyrin, and characterized by elemental analysis, mass spectrometry, UV–vis and dual polarization mode EPR spectroscopy, and electrochemistry. It catalyzed alkene epoxidation and alkane hydroxylation by PhIO and hydroxylation of aromatic compounds by H2O2 in CH2Cl2–CH3CN, as well as hydroxylation of the drug diclofenac by oxone in water. Figure optionsDownload full-size imageDownload as PowerPoint slide