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

Journal Article · Wed Mar 30 04:00:00 EDT 2016 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/jacs.6b00254· OSTI ID:1253828

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

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 data, suggest that the turnover-limiting step features 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. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center, funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. The NSF provided partial support for the EPR instrumentation (NSF CHE-0741901).

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Energy Frontier Research Centers (EFRC) (United States). Center for Molecular Electrocatalysis (CME)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1253828
• Report Number(s): PNNL-SA-111536; KC0307010
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 12 Vol. 138; ISSN 0002-7863
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English