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Kinetics of Electron Transfer Reactions of H_2-Evolving Cobalt Diglyoxime Catalysts

Dempsey, Jillian L. and Winkler, Jay R. and Gray, Harry B. (2010) Kinetics of Electron Transfer Reactions of H_2-Evolving Cobalt Diglyoxime Catalysts. Journal of the American Chemical Society, 132 (3). pp. 1060-1065. ISSN 0002-7863. doi:10.1021/ja9080259.

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Co−diglyoxime complexes catalyze H_2 evolution from protic solutions at modest overpotentials. Upon reduction to Co^I, a Co^(III)-hydride is formed by reaction with a proton donor. Two pathways for H_2 production are analyzed: one is a heterolytic route involving protonation of the hydride to release H_2 and generate Co^(III); the other is a homoytic pathway requiring association of two Co^(III)-hydrides. Rate constants and reorganization parameters were estimated from analyses of laser flash−quench kinetics experiments (Co^(III)−Co^(II) self-exchange k = 9.5 × 10^(−8) − 2.6 × 10^(−5) M^(−1) s^(−1); λ = 3.9 (±0.3) eV: Co^(II)−Co^(I) self-exchange k = 1.2 (±0.5) × 10^5 M^(−1) s^(−1); λ = 1.4 (±0.05) eV). Examination of both the barriers and driving forces associated with the two pathways indicates that the homolytic reaction (Co^(III)H + Co^(III)H → 2 Co^(II) + H_2) is favored over the route that goes through a Co^(III) intermediate (Co^(III)H + H+ → Co^(III) + H_2).

Item Type:Article
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Winkler, Jay R.0000-0002-4453-9716
Gray, Harry B.0000-0002-7937-7876
Additional Information:© 2009 American Chemical Society. Received September 21, 2009. Publication Date (Web): December 31, 2009. We thank Bruce Brunschwig, Xile Hu, Jay Labinger, and Jonas Peters for insightful discussions. We also thank Etsuko Fujita for generous assistance in obtaining in situ absorption spectra. This work was supported by the NSF Center for Chemical Innovation (Powering the Planet, CHE-0802907 and CHE- 0947829), the Arnold and Mabel Beckman Foundation, CCSER (Gordon and Betty Moore Foundation), and the BP MC2 program. JLD is an NSF Graduate Research Fellow.
Group:CCI Solar Fuels
Funding AgencyGrant Number
NSFCHE- 0947829
Arnold and Mabel Beckman FoundationUNSPECIFIED
Gordon and Betty Moore FoundationUNSPECIFIED
Caltech Center for Sustainable Energy ResearchUNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
Issue or Number:3
Record Number:CaltechAUTHORS:20100406-102958526
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Official Citation:Kinetics of Electron Transfer Reactions of H2-Evolving Cobalt Diglyoxime Catalysts Jillian L. Dempsey, Jay R. Winkler, Harry B. Gray Journal of the American Chemical Society 2010 132 (3), 1060-1065
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17867
Deposited By: Ruth Sustaita
Deposited On:06 Apr 2010 20:35
Last Modified:08 Nov 2021 23:39

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