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Molecular mechanisms of cobalt-catalyzed hydrogen evolution

Marinescu, Smaranda C. and Winkler, Jay R. and Gray, Harry B. (2012) Molecular mechanisms of cobalt-catalyzed hydrogen evolution. Proceedings of the National Academy of Sciences of the United States of America, 109 (38). pp. 15127-15131. ISSN 0027-8424. PMCID PMC3458341. doi:10.1073/pnas.1213442109.

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Several cobalt complexes catalyze the evolution of hydrogen from acidic solutions, both homogeneously and at electrodes. The detailed molecular mechanisms of these transformations remain unresolved, largely owing to the fact that key reactive intermediates have eluded detection. One method of stabilizing reactive intermediates involves minimizing the overall reaction free-energy change. Here, we report a new cobalt(I) complex that reacts with tosylic acid to evolve hydrogen with a driving force of just 30 meV∕Co. Protonation of Co^I produces a transient Co^(IIII)-H complex that was characterized by nuclear magnetic resonance spectroscopy. The Co^(IIII)-H intermediate decays by second-order kinetics with an inverse dependence on acid concentration. Analysis of the kinetics suggests that Co^(IIII)-H produces hydrogen by two competing pathways: a slower homolytic route involving two Co^(IIII)-H species and a dominant heterolytic channel in which a highly reactive Co^(II)-H transient is generated by Co^I reduction of Co^(IIII)-H.

Item Type:Article
Related URLs:
URLURL TypeDescription CentralArticle
Marinescu, Smaranda C.0000-0003-2106-8971
Winkler, Jay R.0000-0002-4453-9716
Gray, Harry B.0000-0002-7937-7876
Additional Information:© 2012 National Academy of Sciences. Contributed by Harry B. Gray, August 6, 2012; sent for review July 19, 2012; Published online before print September 4, 2012. We thank Lawrence M. Henling and the late Dr. Michael W. Day for crystallographic assistance, and Dr. Jay A. Labinger for insightful comments. Our work is supported by the National Science Foundation Center for Chemical Innovation in Solar Fuels (CHE-0802907); Center for Chemical Innovation postdoctoral fellowship to S.C.M. We thank Chevron-Phillips for additional support. The Bruker KAPPA APEX II X-ray diffractometer was purchased via a National Science Foundation Chemistry Research Instrumentation and Facilities: Departmental Multi-User Instrumentation (CRIF:MU) award to the California Institute of Technology, CHE-0639094. Author contributions: S.C.M. designed research; S.C.M. performed research; S.C.M. contributed new reagents/analytic tools; S.C.M., J.R.W., and H.B.G. analyzed data; and S.C.M., J.R.W., and H.B.G. wrote the paper. The authors declare no conflict of interest. Data deposition: The atomic coordinates have been deposited in the Cambridge Structural Database, Cambridge Crystallographic Data Centre, Cambridge CB2 1EZ, United Kingdom, [CSD reference numbers 838815 (1), 844589 (2), and 846384 (3)].
Group:CCI Solar Fuels
Funding AgencyGrant Number
Subject Keywords:catalysis; renewable fuel
Issue or Number:38
PubMed Central ID:PMC3458341
Record Number:CaltechAUTHORS:20121022-125521843
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Official Citation:Smaranda C. Marinescu, Jay R. Winkler, and Harry B. Gray Molecular mechanisms of cobalt-catalyzed hydrogen evolution PNAS 2012 109 (38) 15127-15131; published ahead of print September 4, 2012, doi:10.1073/pnas.1213442109
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35009
Deposited On:22 Oct 2012 23:11
Last Modified:09 Nov 2021 23:12

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