Co(salophen)-Catalyzed Aerobic Oxidation of p-Hydroquinone: Mechanism and Implications for Aerobic Oxidation Catalysis
| Autor: | Shannon S. Stahl, Colin W. Anson, Sharon Hammes-Schiffer, Soumya Ghosh |
|---|---|
| Rok vydání: | 2016 |
| Předmět: |
Hydroquinone
010405 organic chemistry Chemistry General Chemistry 010402 general chemistry Photochemistry 01 natural sciences Biochemistry Redox Catalysis 0104 chemical sciences Adduct Metal chemistry.chemical_compound Electron transfer Colloid and Surface Chemistry Mechanism (philosophy) visual_art visual_art.visual_art_medium Density functional theory |
| Zdroj: | Journal of the American Chemical Society. 138:4186-4193 |
| ISSN: | 1520-5126 0002-7863 |
| Popis: | 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 Co(II)(salophen) complex, a Co(III)-superoxide adduct, and a hydrogen-bonded adduct between the hydroquinone and the Co(III)-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 Co(III)-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. |
| Databáze: | OpenAIRE |
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