Electron spin resonance spectra of chloro(N-methyl-5,10,15,20-tetraphenyl-porphinato)copper(II) and manganese(II) complexes. Demethylation mechanism studies

Abstract

ESR spectra of Cu(II) and Mn(II) complexes of N-methyl-5,10,15,20-tetraphenylporphyrin (NCH3TPPH) were studied. A large influence of the pyrrole nitrogen methylation on ESR parameters of Cu(NCH3TPP)Cl and Mn(NCH3TPP)Cl as compared to Cu(TPP) or Mn(TPP) was observed and discussed.The five-coordinate forms of formula Mn(NCH3TPP)X, where X = Cl− or solvent molecule, were defined by characteristic g⊥eff values. The rhombic ESR Hamiltonian (D ≠ 0, E ≠ 0) was accounted for the observed ESR spectra of the five-coordinate forms contrary to the axial one (D ≠ 0, E = 0) for Mn(TPP). Spontaneous demethylation of the Cu(NCH3TPP)Cl complex and formation of Cu(TPP) was observed on the basis of ESR spectra. The decomposition of Mn(NCH3TPP)Cl in the presence of di-n-butylamine (DBA) was analysed. The ESR experimental evidence was found for the presence of Mn(TPP)DBA and Mn(TPP)O2 species as intermediates of this process.