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Title: Benzimidazoles as Metal-Free and Recyclable Hydrides for CO 2 Reduction to Formate

Abstract

We report a novel metal-free chemical reduction of CO 2 by a recyclable benzimidazole-based organo-hydride, whose choice was guided by quantum chemical calculations. Notably, benzimidazole-based hydride donors rival the hydride-donating abilities of noble-metal-based hydrides such as [Ru(tpy)(bpy)H] + and [Pt(depe) 2H] +. Chemical CO 2 reduction to the formate anion (HCOO–) was carried out in the absence of biological enzymes, a sacrificial Lewis acid, or a base to activate the substrate or reductant. 13CO 2 experiments confirmed the formation of H 13COO by CO 2 reduction with the formate product characterized by 1H NMR and 13C NMR spectroscopy and ESI-MS. The highest formate yield of 66% was obtained in the presence of potassium tetrafluoroborate under mild conditions. The likely role of exogenous salt additives in this reaction is to stabilize and shift the equilibrium toward the ionic products. After CO 2 reduction, the benzimidazole-based hydride donor was quantitatively oxidized to its aromatic benzimidazolium cation, establishing its recyclability. In addition, we electrochemically reduced the benzimidazolium cation to its organo-hydride form in quantitative yield, demonstrating its potential for electrocatalytic CO 2 reduction. These results serve as a proof of concept for the electrocatalytic reduction of CO 2 by sustainable, recyclable, andmore » metal-free organo-hydrides.« less

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [1];  [1];  [1]; ORCiD logo [3];  [2]; ORCiD logo [4]
  1. Univ. of Colorado, Boulder, CO (United States)
  2. Univ. of Illinois, Chicago, IL (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
  3. Univ. of Colorado, Boulder, CO (United States); Pasteur Inst., Paris (France)
  4. Univ. of Colorado, Boulder, CO (United States); National Renewable Energy Lab. (NREL), Golden, CO (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
National Science Foundation (NSF); Petroleum Research Fund (PRF); USDOE
OSTI Identifier:
1558602
Grant/Contract Number:  
AC02-06CH11357; CHE-1214131; CHE-1112564; 54436-ND4
Resource Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 141; Journal Issue: 1; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
CO2 reduction; benzimidazole; metal-free; organo-hydride; solar fuels

Citation Formats

Lim, Chern-Hooi, Ilic, Stefan, Alherz, Abdulaziz, Worrell, Brady T., Bacon, Samuel S., Hynes, James T., Glusac, Ksenija D., and Musgrave, Charles B. Benzimidazoles as Metal-Free and Recyclable Hydrides for CO2 Reduction to Formate. United States: N. p., 2018. Web. doi:10.1021/jacs.8b09653.
Lim, Chern-Hooi, Ilic, Stefan, Alherz, Abdulaziz, Worrell, Brady T., Bacon, Samuel S., Hynes, James T., Glusac, Ksenija D., & Musgrave, Charles B. Benzimidazoles as Metal-Free and Recyclable Hydrides for CO2 Reduction to Formate. United States. doi:10.1021/jacs.8b09653.
Lim, Chern-Hooi, Ilic, Stefan, Alherz, Abdulaziz, Worrell, Brady T., Bacon, Samuel S., Hynes, James T., Glusac, Ksenija D., and Musgrave, Charles B. Tue . "Benzimidazoles as Metal-Free and Recyclable Hydrides for CO2 Reduction to Formate". United States. doi:10.1021/jacs.8b09653.
@article{osti_1558602,
title = {Benzimidazoles as Metal-Free and Recyclable Hydrides for CO2 Reduction to Formate},
author = {Lim, Chern-Hooi and Ilic, Stefan and Alherz, Abdulaziz and Worrell, Brady T. and Bacon, Samuel S. and Hynes, James T. and Glusac, Ksenija D. and Musgrave, Charles B.},
abstractNote = {We report a novel metal-free chemical reduction of CO2 by a recyclable benzimidazole-based organo-hydride, whose choice was guided by quantum chemical calculations. Notably, benzimidazole-based hydride donors rival the hydride-donating abilities of noble-metal-based hydrides such as [Ru(tpy)(bpy)H]+ and [Pt(depe)2H]+. Chemical CO2 reduction to the formate anion (HCOO–) was carried out in the absence of biological enzymes, a sacrificial Lewis acid, or a base to activate the substrate or reductant. 13CO2 experiments confirmed the formation of H13COO– by CO2 reduction with the formate product characterized by 1H NMR and 13C NMR spectroscopy and ESI-MS. The highest formate yield of 66% was obtained in the presence of potassium tetrafluoroborate under mild conditions. The likely role of exogenous salt additives in this reaction is to stabilize and shift the equilibrium toward the ionic products. After CO2 reduction, the benzimidazole-based hydride donor was quantitatively oxidized to its aromatic benzimidazolium cation, establishing its recyclability. In addition, we electrochemically reduced the benzimidazolium cation to its organo-hydride form in quantitative yield, demonstrating its potential for electrocatalytic CO2 reduction. These results serve as a proof of concept for the electrocatalytic reduction of CO2 by sustainable, recyclable, and metal-free organo-hydrides.},
doi = {10.1021/jacs.8b09653},
journal = {Journal of the American Chemical Society},
number = 1,
volume = 141,
place = {United States},
year = {2018},
month = {11}
}

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This content will become publicly available on November 27, 2019
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