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Title: Turning on the protonation-first pathway for electrocatalytic CO 2 reduction by manganese bipyridyl tricarbonyl complexes

Electrocatalytic reduction of CO 2 to CO is reported for the complex, { fac-Mn I([(MeO) 2Ph] 2bpy)(CO) 3(CH 3CN)}(OTf), containing four pendant methoxy groups, where [(MeO) 2Ph] 2bpy = 6,6'-bis(2,6-dimethoxyphenyl)-2,2'-bipyridine. In addition to a steric influence similar to that previously established for the 6,6'-dimesityl-2,2'-bipyridine ligand in [ fac-MnI(mes 2bpy)(CO) 3(CH 3CN)](OTf), which prevents Mn 0–Mn 0 dimerization, the [(MeO) 2Ph] 2bpy ligand introduces an additional electronic influence combined with a weak allosteric hydrogen-bonding interaction that significantly lowers the activation barrier for C–OH bond cleavage from the metallocarboxylic acid intermediate. This provides access to the thus far elusive protonation-first pathway, minimizing the required overpotential for electrocatalytic CO 2 to CO conversion by Mn(I) polypyridyl catalysts, while concurrently maintaining a respectable turnover frequency. Comprehensive electrochemical and computational studies here confirm the positive influence of the [(MeO) 2Ph] 2bpy ligand framework on electrocatalytic CO 2 reduction and its dependence upon the concentration and p K a of the external Bronsted acid proton source (water, methanol, trifluoroethanol, and phenol) that is required for this class of manganese catalyst. Linear sweep voltammetry studies show that both phenol and trifluoroethanol as proton sources exhibit the largest protonation-first catalytic currents in combination with { fac-Mn I([(MeO) 2Ph]more » 2bpy)(CO) 3(CH 3CN)}(OTf), saving up to 0.55 V in overpotential with respect to the thermodynamically demanding reduction-first pathway, while bulk electrolysis studies confirm a high product selectivity for CO formation. As a result, to gain further insight into catalyst activation, time-resolved infrared (TRIR) spectroscopy combined with pulse-radiolysis (PR-TRIR), infrared spectroelectrochemistry, and density functional theory calculations were used to establish the v(CO) stretching frequencies and energetics of key redox intermediates relevant to catalyst activation.« less
Authors:
 [1] ;  [1] ;  [1] ;  [1] ; ORCiD logo [2] ;  [2] ; ORCiD logo [1]
  1. Univ. of Massachusetts, Boston, MA (United States)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States)
Publication Date:
Report Number(s):
BNL-113576-2017-JA
Journal ID: ISSN 0002-7863; R&D Project: CO026
Grant/Contract Number:
SC00112704
Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 139; Journal Issue: 7; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; CO2 reduction; electrocatalysis; manganese; pulse radiolysis
OSTI Identifier:
1345736

Ngo, Ken T., McKinnon, Meaghan, Mahanti, Bani, Narayanan, Remya, Grills, David C., Ertem, Mehmed Z., and Rochford, Jonathan. Turning on the protonation-first pathway for electrocatalytic CO2 reduction by manganese bipyridyl tricarbonyl complexes. United States: N. p., Web. doi:10.1021/jacs.6b08776.
Ngo, Ken T., McKinnon, Meaghan, Mahanti, Bani, Narayanan, Remya, Grills, David C., Ertem, Mehmed Z., & Rochford, Jonathan. Turning on the protonation-first pathway for electrocatalytic CO2 reduction by manganese bipyridyl tricarbonyl complexes. United States. doi:10.1021/jacs.6b08776.
Ngo, Ken T., McKinnon, Meaghan, Mahanti, Bani, Narayanan, Remya, Grills, David C., Ertem, Mehmed Z., and Rochford, Jonathan. 2017. "Turning on the protonation-first pathway for electrocatalytic CO2 reduction by manganese bipyridyl tricarbonyl complexes". United States. doi:10.1021/jacs.6b08776. https://www.osti.gov/servlets/purl/1345736.
@article{osti_1345736,
title = {Turning on the protonation-first pathway for electrocatalytic CO2 reduction by manganese bipyridyl tricarbonyl complexes},
author = {Ngo, Ken T. and McKinnon, Meaghan and Mahanti, Bani and Narayanan, Remya and Grills, David C. and Ertem, Mehmed Z. and Rochford, Jonathan},
abstractNote = {Electrocatalytic reduction of CO2 to CO is reported for the complex, {fac-MnI([(MeO)2Ph]2bpy)(CO)3(CH3CN)}(OTf), containing four pendant methoxy groups, where [(MeO)2Ph]2bpy = 6,6'-bis(2,6-dimethoxyphenyl)-2,2'-bipyridine. In addition to a steric influence similar to that previously established for the 6,6'-dimesityl-2,2'-bipyridine ligand in [fac-MnI(mes2bpy)(CO)3(CH3CN)](OTf), which prevents Mn0–Mn0 dimerization, the [(MeO)2Ph]2bpy ligand introduces an additional electronic influence combined with a weak allosteric hydrogen-bonding interaction that significantly lowers the activation barrier for C–OH bond cleavage from the metallocarboxylic acid intermediate. This provides access to the thus far elusive protonation-first pathway, minimizing the required overpotential for electrocatalytic CO2 to CO conversion by Mn(I) polypyridyl catalysts, while concurrently maintaining a respectable turnover frequency. Comprehensive electrochemical and computational studies here confirm the positive influence of the [(MeO)2Ph]2bpy ligand framework on electrocatalytic CO2 reduction and its dependence upon the concentration and pKa of the external Bronsted acid proton source (water, methanol, trifluoroethanol, and phenol) that is required for this class of manganese catalyst. Linear sweep voltammetry studies show that both phenol and trifluoroethanol as proton sources exhibit the largest protonation-first catalytic currents in combination with {fac-MnI([(MeO)2Ph]2bpy)(CO)3(CH3CN)}(OTf), saving up to 0.55 V in overpotential with respect to the thermodynamically demanding reduction-first pathway, while bulk electrolysis studies confirm a high product selectivity for CO formation. As a result, to gain further insight into catalyst activation, time-resolved infrared (TRIR) spectroscopy combined with pulse-radiolysis (PR-TRIR), infrared spectroelectrochemistry, and density functional theory calculations were used to establish the v(CO) stretching frequencies and energetics of key redox intermediates relevant to catalyst activation.},
doi = {10.1021/jacs.6b08776},
journal = {Journal of the American Chemical Society},
number = 7,
volume = 139,
place = {United States},
year = {2017},
month = {1}
}