The catalytic performance of Mn-tetraarylporphyrins in the highly selective oxidation of primary aromatic amines to azo compounds by Bu4NHSO5

Abstract

The catalytic activity of Mn(TPP)OAc/imidazole system in the oxidation of aromatic amines using Bu4NHSO5 in CH3CN, provides a rapid and highly selective method for the preparation of symmetrical azoarenes, in high/excellent yield (78–96%) and short time (<5 min). The selectivity of the reaction depends remarkably on both the axial ligand and the nature of the solvent. Electron-deficient anilines are oxidized slowly and yield azoxy arenes as the main product. The presence of an electron-donating group on the phenyl ring of both the aromatic amine and the porphyrin ligand of the catalyst enhances the oxidative reactivity of the amine as well as the catalytic activity of the Mn-catalyst. The high turn over rates obtained for Mn-porphyrin reflect the efficiency as well as the relative stability of this biomimetic catalyst towards oxidative degradation. Some evidences for the participation of an Mn-oxo species as active oxidant in this catalytic process have been obtained.