Biomimetic alkane oxidation by iodosylbenzene and iodobenzene diacetate catalyzed by a new manganese porphyrin: Water effect

• Synthesis of a novel β-brominated catalyst derived from a non-symmetric porphyrin.
• Water improve product yield in the cyclohexane oxidation by PhIO or PhI(OAc)2.
• Stability of β-brominated catalyst toward oxidative degradation in PhI(OAc)2 systems.

This work describes the synthesis and characterization of the novel third-generation catalyst 5,10-(3,5-bromo,4-aminophenyl)-15,20-(phenyl)-2,3,7,8,12,13,17,18-octabromoporphyrinatomanganese(III) chloride, cis-[MnIIIBr12DAPDPP]Cl, and compares the catalytic activity of this compound with the catalytic activity of the first- and second-generation manganese porphyrins [MnIIITPP]Cl and cis-[MnIIIDAPDPP]Cl, respectively, in cyclohexane, adamantane and n-hexane, oxidation by iodosylbenzene (PhIO) or iodobenzene diacetate (PhI(OAc)2). This work also investigates how addition of water and imidazole influences the catalytic systems in the adamantane and cyclohexane oxidation. In the absence of water and imidazole, cis-[MnIIIBr12DAPDPP]Cl leads to higher product yields as compared with [MnIIITPP]Cl and cis-[MnIIIDAPDPP]Cl in cyclohexane oxidation. The third-generation (β-octabrominated) cis-[MnIIIBr12DAPDPP]Cl was not fully destroyed in reactions with PhI(OAc)2 as oxidant. In the presence of imidazole, [MnIIITPP]Cl and cis-[MnIIIDAPDPP]Cl give superior cyclohexanol yields as compared with cis-[MnIIIBr12DAPDPP]Cl. Addition of water during adamantane oxidation by PhI(OAc)2 increases 1-adamantanol yield. As for cyclohexane oxidation by PhIO or PhI(OAc)2, the presence of water raises product yields and diminishes catalyst destruction, especially in the case of cis-[MnIIIDAPDPP]Cl. The presence of water in systems employing PhI(OAc)2 as oxidant affords higher product yields as compared with systems that use PhIO as oxidant.

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