Chloride Oxidation by Ruthenium Excited-States in Solution

Wehlin, Sara A. M.;Troian-Gautier, Ludovic;Li, Guocan;Meyer, Gerald J.
(2017) Journal of the American chemical society — Vol. 139, n° 37, p. 12903-12906 (2017)

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Abstract
Photodriven HCl splitting to produce solar fuels is an important goal that requires strong photo-oxidants capable of chloride oxidation. In a molecular approach toward this goal, three ruthenium compounds with 2,2′-bipyrazine backbones were found to oxidize chloride ions in acetone solution. Nanosecond transient absorption measurements provide compelling evidence for excited-state electron transfer from chloride to the Ru metal center with rate constants in excess of 1010 M–1 s–1. The Cl atom product was trapped with an olefin. This reactivity was promoted through pre-organization of ground-state precursors in ion pairs. Chloride oxidation with a tetra-cationic ruthenium complex was most favorable, as the dicationic complexes were susceptible to photochemical ligand loss. Marcus analysis afforded an estimate of the chlorine formal reduction potential E°(Cl•/–) = 1.87 V vs NHE that is at least 300 meV more favorable than the accepted values in water.
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Wehlin, S. A. M., Troian-Gautier, L., Li, G., & Meyer, G. J. (2017). Chloride Oxidation by Ruthenium Excited-States in Solution. Journal of the American chemical society, 139(37), 12903-12906. https://doi.org/10.1021/jacs.7b06762 (Original work published 2017)