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Review
. 2010 Dec 8;110(12):6961-7001.
doi: 10.1021/cr100085k. Epub 2010 Oct 6.

Thermochemistry of proton-coupled electron transfer reagents and its implications

Jeffrey J Warren  1 , Tristan A Tronic, James M Mayer
Affiliations
Review

Thermochemistry of proton-coupled electron transfer reagents and its implications

Jeffrey J Warren et al. Chem Rev. .

Erratum in

No abstract available

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Figures

Figure 1
Figure 1
Pourbaix diagram for the in,in-{[RuII(trpy)(H2O)]2(μ-bpp)}3+ water oxidation catalyst (trpy is 2,2′:6′,2″-terpyridine, bpp is bis(2-pyridyl)-3,5-pyrazolate)). Reprinted with permission from Ref. . © 2009 American Chemical Society.
Figure 2
Figure 2
Thermochemistry of the hydroquinone/benzoquinone system (a) in water and (b) in DMSO, from Table 6. Numbers above horizontal arrows give pKa values; numbers beside vertical arrows give electrochemical potentials (vs. NHE in water and vs. Cp2Fe+/0 in DMSO); numbers bisecting diagonal lines are BDFEs in kcal mol−1. In (a), the values in parentheses were estimated by Laviron; in (b) the values in square brackets are estimates using eq 7 and Hess’ Law.
Figure 3
Figure 3
Thermochemistry of the catechol/ortho-quinone system in water, with pKa values above horizontal arrows, redox potentials (in V vs. NHE) beside vertical arrows, and BDFE values (in kcal mol−1) bisecting diagonal lines. The values in square brackets are estimates using eq 7 and Hess’ Law.
Figure 4
Figure 4
Aqueous thermochemistry of ascorbic acid, with pKa values above horizontal arrows, redox potentials (in V vs. NHE) beside vertical arrows, and BDFE values (in kcal mol−1) bisecting diagonal lines. Data from references , , and (see Table 7).
Figure 5
Figure 5
Aqueous PCET thermochemistry of (a) aqueous H2O and (b) aqueous hydrogen peroxide, with pKa values above horizontal arrows, redox potentials (in V vs. NHE) beside vertical arrows, and BDFE values (in kcal mol−1) bisecting diagonal lines.
Figure 6
Figure 6
Frost diagram for dioxygen reduction to water showing the free energy (nE) of the various reactive oxygen species at (a) pH 0 and (b) pH 7. (c) Pourbaix diagram for water, showing the potentials for oxidation to O2 and reduction to H2 as a function of pH and the pressure of O2 and H2 (from M. Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions, reference , with permission, © NACE International 1974).
Figure 7
Figure 7
Double square scheme showing the PCET thermochemistry of flavins. While only one resonance form is drawn for each species, many are better described by multiple structures. Numbers above horizontal arrows give pKa values; numbers beside vertical arrows give electrochemical potentials vs. NHE in water; numbers bisecting diagonal lines are BDFEs in kcal mol−1. The values in square brackets are estimates using eq 7 and Hess’ Law. For definitions of R, see Scheme 10. References for the values in this scheme, and descriptions of how they were derived, are given in the text.
Figure 8
Figure 8
Structures of nicotinamide adenine nucleotide (NADH), nicotinamide adenine dinucleotide phosphate (NADPH) and the model complexes N-benzyl-1,4-dihydronicotinamide (BNAH) and 10-methyl-9,10-dihydroacridine (AcrH2).
Figure 9
Figure 9
Square schemes showing the PCET thermochemistry of 10-methyl-9,10-dihydroacridine (AcrH2) in (a) DMSO and (b) MeCN from Cheng;, see text. Values above horizontal arrows give pKa values; numbers beside vertical arrows give electrochemical potentials vs. Cp2Fe+/0; numbers bisecting diagonal lines are BDFEs in kcal mol−1; and numbers along the steep diagonals are hydride affinities. The values in square brackets are estimates using eq 7 and Hess’ Law. For definitions of R, see Figure 8.
Figure 10
Figure 10
Double square scheme showing the PCET thermochemistry of [cis-(bpy)2(py)RuOHx]n+ from reference(s) and . Numbers above horizontal arrows give pKa values; numbers beside vertical arrows give electrochemical potentials vs. NHE in water; numbers bisecting diagonal lines are BDFEs in kcal mol−1 except for the long diagonal at left which is a hydride affinity, determined following reference . Values in (parentheses) are limits derived from experimental results in .
Figure 11
Figure 11
PCET thermochemistry of the [(phen)4Mn2(O)2]3+ system in MeCN, from reference . The phen ligands are omitted from the formulae for brevity. Numbers above horizontal arrows give pKa values; numbers beside vertical arrows give electrochemical potentials vs. Cp2Fe+/0; numbers bisecting diagonal lines are BDFEs in kcal mol−1 except for the long diagonal at left which is a hydride affinity.
Figure 12
Figure 12
Examples of transition metal PCET systems with three bonds between the redox site and acid/base site. The ancillary ligands in FeIIH2bim and FeIIH2bip are the same as the ligand shown in full. The ancillary O-O ligands are acac (= 2,4-pentanedionato). The black bar in (TPP)FeII(MeImH)2 represents meso-tetraphenylporphyrin.
Figure 13
Figure 13
Potential energy surface showing free energy changes for different mechanisms of H-transfer for the reaction of FeIIH2bim + TEMPO. Not drawn to scale.
Scheme 1
Scheme 1
Concerted vs. stepwise transfer of e− + H+.
Scheme 2
Scheme 2
Hydrogen atom transfer.
Scheme 3
Scheme 3
Concerted proton-electron transfer that is not HAT.
Scheme 4
Scheme 4
Thermochemical square scheme for a PCET reagent.
Scheme 5
Scheme 5
Relationship between gas-phase and solution bond dissociation free energies.
Scheme 6
Scheme 6
Hydroxylamines.
Scheme 7
Scheme 7
Thermochemical analysis of stepwise vs. concerted pathways for the TEMPO + TEMPOH self-exchange reaction.
Scheme 8
Scheme 8
α-Tocopherol (vitamin E) and analogs Trolox C, and HPMC.
Scheme 9
Scheme 9
H• loss and intramolecular H-bonding in ortho-quinones.
Scheme 10
Scheme 10
Nomenclature and structures of biologically relevant flavins.
Scheme 11
Scheme 11
1H+/1e− reaction of guanosine.
Scheme 12
Scheme 12
Thermochemical cycle for transition metal PCET systems.
Scheme 13
Scheme 13
PCET Reactions of High-Valent Heme Species.
Scheme 14
Scheme 14
Ruthenium complexes with large separations between basic and redox sites.
See this image and copyright information in PMC

References

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    1. Cf., Appel AM, Lee S-J, Franz JA, DuBois DL, DuBois MR. J. Am. Chem. Soc. 2009;131:5224.

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