Manganese(III) porphyrins: catalytic activity and intermediate studies in homogeneous systems

Abstract

We studied how solvent, stirring method, PhIO/MnP molar ratio, presence of water and axial ligand affect the catalytic activities of Mn(TPP)Cl, Mn(MNPP)Cl, Mn(TDCPP)Cl and Mn(TFPP)Cl in the oxidation of cyclohexane by PhIO. A study of the catalytic intermediates in the reaction between Mn(TPP)Cl or Mn(TDCPP)Cl and PhIO was also carried out by UV–Vis and EPR spectroscopies. The reaction of Mn(TPP)Cl with PhIO showed the formation of a mixture of species Mn IV(O)P ·+ and Mn V(O)P as intermediates, which were confirmed by the deconvolution of the UV–Vis spectra. Addition of imidazole as cocatalyst favoured the formation of the intermediate species Mn V(O)P, evidenced by the UV–Vis band at 408 nm. The corresponding EPR spectra gave evidence that in the presence of imidazole, Mn IV(O)P ·+ species are formed only in very low amounts. For Mn(TDCPP)Cl the dominating intermediate species is Mn IV(O)P ·+ . Addition of imidazole to halogen-substituted MnP systems does not result in increase of the C-ol yields because very stable bis-imidazole-MnP complexes are formed. Anchoring of such MnP on imidazole propyl gel (IPG) results in better catalytic activity because in this case, the catalyst is mono-coordinated to the support and imidazole favours the formation of the intermediate species Mn V(O)P.