Using combinations of oxidants and bases as PCET reactants: thermochemical and practical considerations

Studies in proton-coupled electron transfer (PCET) often require the combination of an outer-sphere oxidant and a base, to remove an electron and a proton. A common problem is the incompatibility of the oxidant and the base, because the former is electron deficient and the latter electron rich. We h...

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Bibliographic Details
Published in:Energy & environmental science 2012, Vol.5 (7), p.7771-7780
Main Authors: Waidmann, Christopher R, Miller, Alexander JM, Ng, Cheuk-Wa Angela, Scheuermann, Margaret L, Porter, Thomas R, Tronic, Tristan A, Mayer, James M
Format: Article
Language:English
Subjects:
Bonding
Compatibility
Free energy
Incompatibility
Oxidants
Oxidizing agents
Solvents
Stability
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Summary:Studies in proton-coupled electron transfer (PCET) often require the combination of an outer-sphere oxidant and a base, to remove an electron and a proton. A common problem is the incompatibility of the oxidant and the base, because the former is electron deficient and the latter electron rich. We have tested a variety of reagents and report a number of oxidant/base combinations that are compatible and therefore potentially useful as PCET reagents. A formal bond dissociation free energy (BDFE) for a reagent combination is defined by the redox potential of the oxidant and pK sub(a) of the base. This is a formalBDFE because no X-H bond is homolytically cleaved, but it is a very useful way to categorize the H super( times ) accepting ability of an oxidant/base PCET pair. Formal BDFEs of stable oxidant/base combinations range from 71 to at least 98 kcal mol super(-1). Effects of solvent, concentration, temperature, and counterions on the stability of the oxidant/base combinations are discussed. Extensions to catalysis and related reductant/acid combinations are mentioned.
ISSN:1754-5692
1754-5706
DOI:10.1039/c2ee03300c