Shannon Stahl, Ph.D.
Speaker's Institution
University of Wisconsin, Madison
Chemistry A101
Mixer Time
Mixer Time
Chemistry B101E
Calendar (ICS) Event
Additional Information

About the Seminar:

Liquid phase aerobic oxidations in chemistry and biology feature a variety of different mechanisms for O2 activation and use as an oxidant. Radical-chain mechanisms involve the formation organic radicals that react directly with O2. Monooxygenase enzymes feature reductive activation of O2 to generate a reactive two-electron oxidant, such as a metal-oxo species, that promotes oxygen-atom transfer to an organic molecule. Many homogeneous and heterogeneous catalysts for aerobic oxidation promote mechanisms similar to oxidase enzymes that couple two redox half-reactions consisting of (i) the two- or four-electron oxygen reduction reaction (ORR) and (ii) oxidation of an organic substrate. This oxidase-type mechanism resembles redox reactions in electrochemistry and fuel cells, drawing attention to the issue of ORR “overpotential” in synthetic reactions ((Stamoulis et al. J. Am. Chem. Soc. 2023, 145, 17515-17526). In fuel cells, the ORR overpotential (hORR) influences the accessible cell potential (Ecell, Figure A). In aerobic oxidations, the thermodynamic efficiency of the ORR step (hORR), directly impacting the thermodynamic driving force available for oxidation of the substrate (hsub). Manifestations of these concepts differ for homogeneous and heterogeneous catalysts. This talk will discuss the implications of the dioxygen activation mechanism and ORR overpotential in liquid-phase aerobic oxidation reactions, including both homogeneous and heterogeneous catalysts. Homogeneous catalysts often exhibit high hORR that limits the scope of accessible reactivity.

More information about the speaker and his research group can be found here.