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

Abstract 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 CH 3 CN). 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 H 2 O 2 in CH 2 Cl 2 /CH 3 CN, 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.