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Electrophilic Arene Hydroxylation and Phenol OH Oxidations Performed by an Unsymmetric µ-[eta]1:[eta]1-O2-Peroxo Dicopper(II) Complex

Chemistry : a European journal, 2012-02, Vol.18 (7), p.2113 [Peer Reviewed Journal]

ISSN: 0947-6539 ;EISSN: 1521-3765 ;DOI: 10.1002/chem.201102372 ;CODEN: CEUJED

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  • Title:
    Electrophilic Arene Hydroxylation and Phenol OH Oxidations Performed by an Unsymmetric µ-[eta]1:[eta]1-O2-Peroxo Dicopper(II) Complex
  • Author: Garcia-Bosch, Isaac ; Ribas, Xavi ; Costas, Miquel
  • Subjects: Phenols
  • Is Part Of: Chemistry : a European journal, 2012-02, Vol.18 (7), p.2113
  • Description:   Reactions of the unsymmetric dicopper(II) peroxide complex [CuII2(µ-η1:η1-O2)(m-XYLN3N4)]2+ (1O2, where m-XYL is a heptadentate N-based ligand), with phenolates and phenols are described. Complex 1O2 reacts with p-X-PhONa (X=MeO, Cl, H, or Me) at -90°C performing tyrosinase-like ortho-hydroxylation of the aromatic ring to afford the corresponding catechol products. Mechanistic studies demonstrate that reactions occur through initial reversible formation of metastable association complexes [CuII2(µ-η1:η1-O2)(p-X-PhO)(m-XYLN3N4)]+ (1O2X-PhO) that then undergo ortho-hydroxylation of the aromatic ring by the peroxide moiety. Complex 1O2 also reacts with 4-X-substituted phenols p-X-PhOH (X=MeO, Me, F, H, or Cl) and with 2,4-di-tert-butylphenol at -90°C causing rapid decay of 1O2 and affording biphenol coupling products, which is indicative that reactions occur through formation of phenoxyl radicals that then undergo radical CC coupling. Spectroscopic UV/Vis monitoring and kinetic analysis show that reactions take place through reversible formation of ground-state association complexes [CuII2(µ-η1:η1-O2)(X-PhOH)(m-XYLN3N4)]2+ (1O2X-PhOH) that then evolve through an irreversible rate-determining step. Mechanistic studies indicate that 1O2 reacts with phenols through initial phenol binding to the Cu2O2 core, followed by a proton-coupled electron transfer (PCET) at the rate-determining step. Results disclosed in this work provide experimental evidence that the unsymmetric 1O2 complex can mediate electrophilic arene hydroxylation and PCET reactions commonly associated with electrophilic Cu2O2 cores, and strongly suggest that the ability to form substrateCu2O2 association complexes may provide paths to overcome the inherent reactivity of the O2-binding mode. This work provides experimental evidence that the presence of a H+ completely determines the fate of the association complex [CuII2(µ-η1:η1-O2)(X-PhO(H))(m-XYLN3N4)]n+ between a PCET and an arene hydroxylation reaction, and may provide clues to help understand enzymatic reactions at dicopper sites.
  • Publisher: Weinheim: Wiley Subscription Services, Inc
  • Language: English
  • Identifier: ISSN: 0947-6539
    EISSN: 1521-3765
    DOI: 10.1002/chem.201102372
    CODEN: CEUJED
  • Source: Alma/SFX Local Collection
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