New manganese porphyrin as biomimetic catalyst of cyclohexane oxidation: Effect of water or imidazole as additives

• Synthesis of a novel β-brominated catalyst derived from a non-symmetric porphyrin.
• Water acting as an efficient additive in cyclohexane oxidation by PhIO.
• Stability of β-brominated catalyst toward oxidative degradation in PhI(OAc)2 systems.

This work describes the synthesis and characterization of the novel catalyst 5-(3-bromo,4-amino)phenyl-10,15,20-trisphenyl-2,3,7,8,12,13,17,18-octabromoporphyrinmanganese(III) chloride (MnIIIBr9APTPPCl). This compound, MnIIIAPTPPCl and MnIIITPPCl were employed as catalysts in cyclohexane oxidation using PhIO or PhI(OAc)2 as oxidants. In the reactions with PhIO and PhI(OAc)2, MnIIIBr9APTPPCl led to higher yields of products compared to the other catalysts. Furthermore, for the first time it was observed a recovery of the third generation (β-octabrominated) catalyst in reactions using PhI(OAc)2 as oxidant. Reactions were performed with the addition of imidazole or water as additives. The reactions with imidazole showed higher yields for cyclohexanol in all systems studied. For systems using PhIO it was also observed a decrease of catalysts oxidative destruction. All the systems using PhIO and water led to an increase in product yield. However, the recovery of catalyst was low for almost all these systems. Nevertheless, this is the first work to show the role of water as an effective additive in the oxidation of cyclohexane catalyzed by manganese porphyrins.

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