A high-valent manganese(IV)-hydroxo porphyrinπ-cation radical complex,[Mn^(IV)(OH)(Por^(˙+))(OTf)]^(+)(a protonated manganese compound I analogue),was studied in the halogenation of aromatic compounds.By replacing t...A high-valent manganese(IV)-hydroxo porphyrinπ-cation radical complex,[Mn^(IV)(OH)(Por^(˙+))(OTf)]^(+)(a protonated manganese compound I analogue),was studied in the halogenation of aromatic compounds.By replacing the triflate anion with Cl^(-)or Br^(-),we were able to halogenate toluene with high selectivity for C(sp^(2))-H bonds over C(sp^(3))-H bonds,such as chlorination with Cl^(-)or bromination with Br^(-)in the aromatic ring.We have also examined the halogenation of naphthalene and benzene derivatives with[Mn^(IV)(OH)(Por^(˙+))(X)]^(+)(X=Cl^(-)and Br^(-)).In all of these reactions,halogenated products were formed dominantly,and the source of the halogens in the products was found to be halides present in the[Mn^(IV)(OH)(Por^(˙+))(X)]^(+)complexes.In the absence of halides,naphthalene was found to undergo dimerization.Kinetic isotope effect(KIE)experiments on this reaction showed no isotopic effect in the halogenation reactions.DFT calculations on models with the naphthalene substrate supported a mechanism involving an initial(rate-limiting)electron transfer from the substrate to[Mn^(IV)(OH)(Por^(˙+))(OTf)]^(+),coupled by the attachment of Cl^(-)to the C1 position of the naphthalene radical cation.This mechanism was also supported by the Marcus theory of outer-sphere electron transfer.The so-formed[Mn^(IV)(OH)(Por)(OTf)](a manganese compound II analogue)underwent a hydrogen atom transfer from the C1 position of the substrate to form chlorinated naphthalene and[Mn^(III)(H_(2)O)(Por)(OTf)].DFT calculations showed that[Mn^(IV)(OH)(Por)(OTf)]can also undergo direct OH-transfer to the substrate competitively,leaving open possibilities for side reactions or alternative reactions in a different environment.This study provides a deeper understanding of chloroperoxidase-like reactions.展开更多
基金supported by the NRF of Korea(NRF-2021R1A3B1076539 and NRF-2023K2A9A2A11098996 to W.N.,NRF-2023R1A2C1007668 to Y.-M.L.and RS-2021-NR058689 to K.-B.C.)the MoE G-LAMP Program(No.RS-2024-00443714 to K.-B.C)the Henan Center for Outstanding Overseas Scientists,China(GZS2024020 to W.N.).
文摘A high-valent manganese(IV)-hydroxo porphyrinπ-cation radical complex,[Mn^(IV)(OH)(Por^(˙+))(OTf)]^(+)(a protonated manganese compound I analogue),was studied in the halogenation of aromatic compounds.By replacing the triflate anion with Cl^(-)or Br^(-),we were able to halogenate toluene with high selectivity for C(sp^(2))-H bonds over C(sp^(3))-H bonds,such as chlorination with Cl^(-)or bromination with Br^(-)in the aromatic ring.We have also examined the halogenation of naphthalene and benzene derivatives with[Mn^(IV)(OH)(Por^(˙+))(X)]^(+)(X=Cl^(-)and Br^(-)).In all of these reactions,halogenated products were formed dominantly,and the source of the halogens in the products was found to be halides present in the[Mn^(IV)(OH)(Por^(˙+))(X)]^(+)complexes.In the absence of halides,naphthalene was found to undergo dimerization.Kinetic isotope effect(KIE)experiments on this reaction showed no isotopic effect in the halogenation reactions.DFT calculations on models with the naphthalene substrate supported a mechanism involving an initial(rate-limiting)electron transfer from the substrate to[Mn^(IV)(OH)(Por^(˙+))(OTf)]^(+),coupled by the attachment of Cl^(-)to the C1 position of the naphthalene radical cation.This mechanism was also supported by the Marcus theory of outer-sphere electron transfer.The so-formed[Mn^(IV)(OH)(Por)(OTf)](a manganese compound II analogue)underwent a hydrogen atom transfer from the C1 position of the substrate to form chlorinated naphthalene and[Mn^(III)(H_(2)O)(Por)(OTf)].DFT calculations showed that[Mn^(IV)(OH)(Por)(OTf)]can also undergo direct OH-transfer to the substrate competitively,leaving open possibilities for side reactions or alternative reactions in a different environment.This study provides a deeper understanding of chloroperoxidase-like reactions.
