Organic molecules to probe PCET fundamentals

Our laboratory has developed systems to examine PCET oxidations of phenols and related molecules in detail. We are constructing phenols with intramolecular hydrogen bonds, so that upon oxidation of the phenol portion the proton moves in a very controlled way. In the example below, the phenol transfers an electron to an oxidant A+ concerted with proton transfer to a pyridine. The oxidant could be an organic or inorganic reagent, or a photochemical excited state. The advantage of photoinduced MS-CPET is that very fast processes can be studied. These molecules are in some ways models for the archetypal example of MS-CPET is the redox active tyrosine Z in Photosystem II. Our systems have provided insights into the dependence of MS-CPET reactions on driving force (the sum of the electron transfer and proton transfer energetics), on the Marcus intrinsic barriers (rearrangements that occur in concert with MS-CPET), and the nature of the hydrogen bond. As shown in the figure below, stronger H-bonds – as indicated by lower ν(OH) – exhibit faster CPET rates.

Relevant Publications

Agarwal, R. G.; Coste, S. C.; Groff, B. D.; Heuer, A. M.; Noh, H.; Parada, G. A.; Wise, C. F.; Nichols, E. M.; Warren, J. J.; Mayer, J. M.
Free Energies of Proton-Coupled Electron Transfer Reagents and Their Applications
Chem. Rev.  2022122, 1-49.  
Cotter, L. F.; Rimgard, B. P.; Parada, G. A.; Mayer, J. M.; Hammarström, L.
Solvent and temperature effects on photoinduced proton-coupled electron transfer in the Marcus inverted region
J. Phys. Chem. A  2021125, 7670–7684.  
Coste, S. C.; Brezny, A. C.; Koronkiewicz, B. K.; Mayer, J. M.
C–H Oxidation in Fluorenyl Benzoates Does Not Proceed Through a Stepwise Pathway: Revisiting Asynchronous Proton-Coupled Electron Transfer
Chem. Sci.  202112, 13127-13136.  
Salamone, M.; Van Santen, J.; Montalvo, E. R.; Galeotti, M.; Groff, B. D.; Mayer, J. M.; DiLabio, G. A.; Bietti, M.
Bimodal Evans−Polanyi Relationships in Hydrogen Atom Transfer from C(sp3)–H Bonds to the Cumyloxyl Radical. A Combined Time-Resolved Kinetic and Computational Study
J. Am. Chem. Soc.  2021143, 11759–11776.  
Kolmar, S. S.; Mayer, J. M.
SmI2(H2O)n Reductions of Electron Rich Enamines by Concerted Proton-Coupled Electron Transfer
J. Am. Chem. Soc.  2017139, 10687-10692.  
Morris, W. D.; Mayer, J. M.
Separating Proton and Electron Transfer Effects in Three-Component Concerted PCET Reactions
J. Am. Chem. Soc.  2017139, 10312-10319.  
Cattaneo, M.; Ryken, S. A.; Mayer, J. M.
Outer-Sphere 2 e/2 H+ Transfer Reactions of Ruthenium(II)-Amine and Ruthenium(IV)-Amido Complexes
Angew. Chem. Int. Ed.  201756, 3675-3678.  
Schrauben, J.N.; Cattaneo, M.; Day, T.C.; Tenderholt, A.L.; Mayer, J.M.
Multiple-Site Concerted Proton-Electron Transfer Reactions of Hydrogen-Bonded Phenols are Non-adiabatic and Well Described by Semi-Classical Marcus Theory
J. Am. Chem. Soc.   2012134, 16635-16645.  
Markle, T.F.; Rhile, I.J.; DiPasquale, A.G.; Mayer, J.M.
Probing Concerted Proton-Electron Transfer in Phenol-Imidazoles
Proc. Natl. Acad. Sci.   2008105, 8185-8190.  
Markle, T.F.; Mayer, J.M.
Concerted Proton-Electron Transfer in Pyridylphenols: The Importance of the Hydrogen Bond
Angew. Chem., Int. Ed.   200847, 738-740.