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Cobalt meso-Tetrakis(N-methyl-4-pyridiniumyl)porphyrin Becomes a Catalyst for the Electroreduction of O_2 by Four Electrons When [(NH_3)_5Os]^(n+) (n = 2, 3) Groups Are Coordinated to the Porphyrin Ring

Shi, Chunnian and Anson, Fred C. (1996) Cobalt meso-Tetrakis(N-methyl-4-pyridiniumyl)porphyrin Becomes a Catalyst for the Electroreduction of O_2 by Four Electrons When [(NH_3)_5Os]^(n+) (n = 2, 3) Groups Are Coordinated to the Porphyrin Ring. Inorganic Chemistry, 35 (26). pp. 7928-7931. ISSN 0020-1669. http://resolver.caltech.edu/CaltechAUTHORS:20180525-133925688

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Abstract

In a series of recent reports evidence has been offered to support the proposal that coordination of (NH_3)_5Ru^(2+) groups to ligand sites introduced on the meso positions of certain cobalt porphyrins enhances their abilities to act as electrocatalysts for the reduction of O_2 to H_2O. The enhancement is believed to be the result of back-bonding by the Ru(II) centers into the pendant ligands and the cobalt porphyrin to which they are linked. The catalytic mechanism that has been proposed leaves the coordinated Ru centers in their +2 oxidation state as the O_2 molecule coordinated to the Co(II) center of the porphyrin in the activated complex is reduced via electron-transfer from the electrode surface. Intramolecular electron-transfer from the Ru(II) centers to the coordinated O_2 is not consistent with the experimental data. To obtain additional information about the importance of back-bonding in enhancing the catalytic activity of these cobalt porphyrins, we sought to use Os(III) in place of Ru(II) as the source of the back-donation. Os(III), unlike Ru(III), exhibits substantial back-bonding capabilities, but Os(III) is a much weaker thermodynamic reductant than Ru(II). Thus, we reasoned that any increase in the catalytic activity of cobalt porphyrins that might result from the attachment of Os(III) centers to the porphyrin ring could be confidently attributed to back-bonding effects free of any contributions from intramolecular electron-transfer. The results of experiments designed to test this speculation are described in this report.


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https://dx.doi.org/10.1021/ic9607189DOIArticle
Alternate Title:Cobalt meso-Tetrakis(N-methyl-4-pyridiniumyl)porphyrin Becomes a Catalyst for the Electroreduction of O2 by Four Electrons When [(NH3)5Os]n+ (n = 2, 3) Groups Are Coordinated to the Porphyrin Ring
Additional Information:© 1996 American Chemical Society. Received June 14, 1996. This work was supported by the National Science Foundation. Helpful suggestions from Prof. W. D. Harmon were appreciated.
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Record Number:CaltechAUTHORS:20180525-133925688
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20180525-133925688
Official Citation:Cobalt meso-Tetrakis(N-methyl-4-pyridiniumyl)porphyrin Becomes a Catalyst for the Electroreduction of O2 by Four Electrons When [(NH3)5Os]n+ (n = 2, 3) Groups Are Coordinated to the Porphyrin Ring Chunnian Shi and Fred C. Anson Inorganic Chemistry 1996 35 (26), 7928-7931 DOI: 10.1021/ic9607189
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ID Code:86634
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:25 May 2018 20:49
Last Modified:25 May 2018 20:49

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