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DFT study of an unusual proton-relay role for Cp* in hydrogen evolution catalysis

Johnson, Samantha I. and Corona, Sydney L. and Blakemore, James D. and Winkler, Jay R. and Gray, Harry B. and Goddard, William A. (2016) DFT study of an unusual proton-relay role for Cp* in hydrogen evolution catalysis. In: 251st American Chemical Society National Meeting & Exposition, March 13-17, 2016, San Diego, CA.

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Understanding mechanisms of the hydrogen evolution reaction (HER) is crucial to designing efficient catalysts for the prodn. of solar fuels. Cp*Rh(bpy) (Cp* = η^5- pentamethylcyclopentadienyl; bpy = κ^2-2,2'- bipyridyl) generates hydrogen in the presence of acid. However, the nature of the elementary steps leading to H-H formation has not been clear, as chem. characterization of intermediates in the catalytic reaction has been difficult to obtain. Here, we present a joint exptl.- computational study that addresses this challenge. D. functional theory (DFT) calcns. demonstrate that the catalyst first undergoes a 2e- redn. to form a Rh^I complex. Subsequently, in presence of acid, the Rh complex undergoes protonation at the Cp* ligand to form a complex bearing an [η^4-Cp*H] ligand, preserving the RhI center. DFT calcns. show that this complex is 6.8 kcal /mol more stable than the analogous Rh^(III) hydride. Following the formation of this intermediate, a second protonation can be carried out which results in evolution of hydrogen and restoration of η^5-Cp*. To the best of our knowledge, these results are among the first to show Cp* can serve as a proton relay in HER. New DFT results on the full mechanism for this compd. will be presented, and predictions of possible improvements to the catalyst will be discussed in light of the newly characterized intermediate.

Item Type:Conference or Workshop Item (Paper)
Related URLs:
URLURL TypeDescription Website
Blakemore, James D.0000-0003-4172-7460
Winkler, Jay R.0000-0002-4453-9716
Gray, Harry B.0000-0002-7937-7876
Goddard, William A.0000-0003-0097-5716
Additional Information:© 2016 American Chemical Society.
Record Number:CaltechAUTHORS:20160413-110622091
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:66114
Deposited By: Tony Diaz
Deposited On:13 Apr 2016 18:12
Last Modified:22 Nov 2019 09:58

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