Exploring manganese pyridylporphyrin isomers for cyclohexane oxidation: First‐generation catalysts are better than third‐generation ones

Abstract

AbstractManganese porphyrins are widely studied as catalysts for oxidation reactions of different organic substrates. In this work, we evaluate the catalytic activity of manganese complexes derived from meso‐tetrakis(2‐, 3‐, or 4‐pyridyl) porphyrin isomers, [Mn(TXPyP)]Cl (X = 2, 3, or 4), and the respective β‐octabrominated counter‐parts, [Mn(Br8TXPyP)], for oxidation of cyclohexane by PhI(OAc)2. At first, we describe the synthesis and characterization of a new third‐generation manganese porphyrin, [Mn(Br8T4PyP)]. It presented a more positive value of half‐wave potential (−0.287 V vs. Fc+/Fc) and a lower solubility in organic solvents among the isomers. In general, the third‐generation catalysts [Mn(Br8TXPyP)] showed lower catalytic activity than those of the first‐generation [Mn(TXPyP)]Cl in all systems studied. In addition, the use of water or imidazole as cocatalysts did not increase the yield or selectivity of the systems. Finally, when evaluating the use of the classic oxidant PhIO, there was a decrease in yield for all systems, indicating that PhI(OAc)2 is a good substitute for this oxidant in catalytic systems.