Journal
CHEMICAL SCIENCE
Volume 4, Issue 4, Pages 1578-1587Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c3sc22239j
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Funding
- DOE/LBNL grant [403801]
- NSF Grant [CHE-1111900]
- Miller Institute for Basic Research
- National Science Foundation
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1111900] Funding Source: National Science Foundation
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The pentapyridine cobalt complex [Co(PY5Me(2))](2+) and its congeners have been shown to catalyze proton reduction to hydrogen in aqueous solution over a wide pH range using electrical or solar energy input. Here, we employ electrochemical and spectroscopic studies to examine the mechanisms of proton reduction by this parent complex under soluble, diffusion-limited conditions in acetonitrile with acetic acid as the proton donor. Two pathways for proton reduction are identified via cyclic voltammetry: one pathway occurring from an acetonitrile-bound Co-II/I couple and the other pathway operating from an acetate-bound Co-II/I couple. Kinetics studies support protonation of a Co-I species as the rate-determining step for both processes, and additional electrochemical measurements further suggest that the onset of catalysis from the acetonitrile-bound Co-II/I couple is highly affected by catalyst electronics. Taken together, this work not only establishes the CoPY5Me(2) unit as a unique molecular platform that catalyzes the reduction of protons under soluble, diffusion-limited conditions in both aqueous and organic media, but also highlights the participation of anation processes that are likely relevant for a wide range of hydrogen-producing and related catalytic systems.
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