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Title: Controlling Proton Delivery with Catalyst Structural Dynamics

Abstract

The fastest synthetic molecular catalysts for production and oxidation of H2 emulate components of the active site of natural hydrogenases. The role of controlled structural dynamics is recognized as a critical component in the catalytic performance of many enzymes, including hydrogenases, but is largely neglected in the design of synthetic molecular cata-lysts. In this work, the impact of controlling structural dynamics on the rate of production of H2 was studied for a series of [Ni(PPh2NC6H4-R2)2]2+ catalysts including R = n-hexyl, n-decyl, n-tetradecyl, n-octadecyl, phenyl, or cyclohexyl. A strong correlation was observed between the ligand structural dynamics and the rates of electrocatalytic hydrogen production in acetonitrile, acetonitrile-water, and protic ionic liquid-water mixtures. Specifically, the turnover frequencies correlate inversely with the rates of ring inversion of the amine-containing ligand, as this dynamic process dictates the positioning of the proton relay in the second coordination sphere and therefore governs protonation at either catalytically productive or non-productive sites. This study demonstrates that the dynamic processes involved in proton delivery can be controlled through modifications of the outer coordination sphere of the catalyst, similar to the role of the protein architecture in many enzymes. The present work provides new mechanistic insight into the large ratemore » enhancements observed in aqueous protic ionic liquid media for the [Ni(PPh2NR2)]2+ family of catalysts. The incorporation of controlled structural dynamics as a design parameter to modulate proton delivery in molecular catalysts has enabled H2 production rates that are up to three orders of magnitude faster than the [Ni(PPh2NPh2)]2+complex. The observed turnover frequencies are up to 106 s-1 in acetonitrile-water, and over 107 s-1 in protic ionic liquid-water mixtures, with a minimal increase in overpotential. This material is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, and was performed in part using the Molecular Science Computing Facility (MSCF) in the William R. Wiley Environmental Molecular Sciences Laboratory, a DOE national scientific user facility located at Pacific Northwest National Laboratory (PNNL). PNNL is operated by Battelle for DOE.« less

Authors:
 [1];  [1]; ORCiD logo [1];  [1];  [1];  [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]
  1. BATTELLE (PACIFIC NW LAB)
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1513213
Report Number(s):
PNNL-SA-115082
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Angewandte Chemie International Edition
Additional Journal Information:
Journal Volume: 55; Journal Issue: 43
Country of Publication:
United States
Language:
English
Subject:
electrocatalysis, structural dynamics

Citation Formats

Cardenas, Allan J., Ginovska-Pangovska, Bojana, Kumar, Neeraj, Hou, Jianbo, Raugei, Simone, Helm, Monte L., Appel, Aaron M., Bullock, Ronald M., and O'Hagan, Molly J. Controlling Proton Delivery with Catalyst Structural Dynamics. United States: N. p., 2016. Web. doi:10.1002/anie.201607460.
Cardenas, Allan J., Ginovska-Pangovska, Bojana, Kumar, Neeraj, Hou, Jianbo, Raugei, Simone, Helm, Monte L., Appel, Aaron M., Bullock, Ronald M., & O'Hagan, Molly J. Controlling Proton Delivery with Catalyst Structural Dynamics. United States. doi:10.1002/anie.201607460.
Cardenas, Allan J., Ginovska-Pangovska, Bojana, Kumar, Neeraj, Hou, Jianbo, Raugei, Simone, Helm, Monte L., Appel, Aaron M., Bullock, Ronald M., and O'Hagan, Molly J. Mon . "Controlling Proton Delivery with Catalyst Structural Dynamics". United States. doi:10.1002/anie.201607460.
@article{osti_1513213,
title = {Controlling Proton Delivery with Catalyst Structural Dynamics},
author = {Cardenas, Allan J. and Ginovska-Pangovska, Bojana and Kumar, Neeraj and Hou, Jianbo and Raugei, Simone and Helm, Monte L. and Appel, Aaron M. and Bullock, Ronald M. and O'Hagan, Molly J.},
abstractNote = {The fastest synthetic molecular catalysts for production and oxidation of H2 emulate components of the active site of natural hydrogenases. The role of controlled structural dynamics is recognized as a critical component in the catalytic performance of many enzymes, including hydrogenases, but is largely neglected in the design of synthetic molecular cata-lysts. In this work, the impact of controlling structural dynamics on the rate of production of H2 was studied for a series of [Ni(PPh2NC6H4-R2)2]2+ catalysts including R = n-hexyl, n-decyl, n-tetradecyl, n-octadecyl, phenyl, or cyclohexyl. A strong correlation was observed between the ligand structural dynamics and the rates of electrocatalytic hydrogen production in acetonitrile, acetonitrile-water, and protic ionic liquid-water mixtures. Specifically, the turnover frequencies correlate inversely with the rates of ring inversion of the amine-containing ligand, as this dynamic process dictates the positioning of the proton relay in the second coordination sphere and therefore governs protonation at either catalytically productive or non-productive sites. This study demonstrates that the dynamic processes involved in proton delivery can be controlled through modifications of the outer coordination sphere of the catalyst, similar to the role of the protein architecture in many enzymes. The present work provides new mechanistic insight into the large rate enhancements observed in aqueous protic ionic liquid media for the [Ni(PPh2NR2)]2+ family of catalysts. The incorporation of controlled structural dynamics as a design parameter to modulate proton delivery in molecular catalysts has enabled H2 production rates that are up to three orders of magnitude faster than the [Ni(PPh2NPh2)]2+complex. The observed turnover frequencies are up to 106 s-1 in acetonitrile-water, and over 107 s-1 in protic ionic liquid-water mixtures, with a minimal increase in overpotential. This material is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, and was performed in part using the Molecular Science Computing Facility (MSCF) in the William R. Wiley Environmental Molecular Sciences Laboratory, a DOE national scientific user facility located at Pacific Northwest National Laboratory (PNNL). PNNL is operated by Battelle for DOE.},
doi = {10.1002/anie.201607460},
journal = {Angewandte Chemie International Edition},
number = 43,
volume = 55,
place = {United States},
year = {2016},
month = {10}
}

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