Co(salophen)-Catalyzed Aerobic Oxidation of p-Hydroquinone: Mechanism and Implications for Aerobic Oxidation Catalysis

Colin W. Anson, Soumya Ghosh, Sharon Hammes-Schiffer, Shannon S. Stahl

Research output: Contribution to journalArticlepeer-review

Abstract

Macrocyclic metal complexes and p-benzoquinones are commonly used as co-catalytic redox mediators in aerobic oxidation reactions. In an effort to gain insight into the mechanism and energetic efficiency of these reactions, we investigated Co(salophen)-catalyzed aerobic oxidation of p-hydroquinone. Kinetic and spectroscopic data suggest that the catalyst resting-state consists of an equilibrium between a CoII(salophen) complex, a CoIII-superoxide adduct, and a hydrogen-bonded adduct between the hydroquinone and the CoIII-O2 species. The kinetic data, together with density functional theory computational results, reveal that the turnover-limiting step involves proton-coupled electron transfer from a semi-hydroquinone species and a CoIII-hydroperoxide intermediate. Additional experimental and computational data suggest that a coordinated H2O2 intermediate oxidizes a second equivalent of hydroquinone. Collectively, the results show how Co(salophen) and p-hydroquinone operate synergistically to mediate O2 reduction and generate the reactive p-benzoquinone co-catalyst.

Original languageEnglish (US)
Pages (from-to)4186-4193
Number of pages8
JournalJournal of the American Chemical Society
Volume138
Issue number12
DOIs
StatePublished - Apr 20 2016

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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