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Title: Direct Observation by Rapid-Scan FT-IR Spectroscopy of Two-Electron-Reduced Intermediate of Tetraaza Catalyst [Co IIN 4H(MeCN)] 2+ Converting CO 2 to CO

Abstract

In the search for the two-electron-reduced intermediate of the tetraaza catalyst [Co IIN 4H(MeCN)] 2+ (N 4H = 2,12-dimethyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),2,11,13,15-pentaene) for CO 2 reduction and elementary steps that result in the formation of CO product, rapid-scan FT-IR spectroscopy of the visible-light-sensitized catalysis, using Ir(ppy) 3 in wet acetonitrile (CD 3CN) solution, led to the observation of two sequential intermediates. The initially formed one-electron-reduced [Co IN 4H] +--CO 2 adduct was converted by the second electron to a transient [Co IN 4H] +--CO 2 - complex that spontaneously converted CO 2 to CO in a rate-limiting step on the second time scale in the dark under regeneration of the catalyst (room temperature). The macrocycle IR spectra of the [Co IN 4H] +--CO 2 - complex and the preceding one-electron [Co IN 4H] +--CO 2 intermediate show close similarity but distinct differences in the carboxylate modes, indicating that the second electron resides mainly on the CO 2 ligand. Vibrational assignments are corroborated by 13C isotopic labeling. The structure and stability of the two-electron-reduced intermediate derived from the time-resolved IR study are in good agreement with recent predictions by DFT electronic structure calculations. This is the first observation of an intermediate of a molecularmore » catalyst for CO 2 reduction during the bond-breaking step producing CO. The reaction pathway for the Co tetraaza catalyst uncovered here suggests that the competition between CO 2 reduction and proton reduction of a macrocyclic multi-electron catalyst is steered toward CO 2 activation if the second electron is directly captured by an adduct of CO 2 and the one-electron-reduced catalyst intermediate.« less

Authors:
 [1];  [1]
  1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Biophysics and integrated Bioimaging Division
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1378345
DOE Contract Number:  
AC02-05CH11231; SC0004993
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of the American Chemical Society; Journal Volume: 138; Journal Issue: 31
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Sheng, Hua, and Frei, Heinz. Direct Observation by Rapid-Scan FT-IR Spectroscopy of Two-Electron-Reduced Intermediate of Tetraaza Catalyst [CoIIN4H(MeCN)]2+ Converting CO 2 to CO. United States: N. p., 2016. Web. doi:10.1021/jacs.6b05248.
Sheng, Hua, & Frei, Heinz. Direct Observation by Rapid-Scan FT-IR Spectroscopy of Two-Electron-Reduced Intermediate of Tetraaza Catalyst [CoIIN4H(MeCN)]2+ Converting CO 2 to CO. United States. doi:10.1021/jacs.6b05248.
Sheng, Hua, and Frei, Heinz. Fri . "Direct Observation by Rapid-Scan FT-IR Spectroscopy of Two-Electron-Reduced Intermediate of Tetraaza Catalyst [CoIIN4H(MeCN)]2+ Converting CO 2 to CO". United States. doi:10.1021/jacs.6b05248.
@article{osti_1378345,
title = {Direct Observation by Rapid-Scan FT-IR Spectroscopy of Two-Electron-Reduced Intermediate of Tetraaza Catalyst [CoIIN4H(MeCN)]2+ Converting CO 2 to CO},
author = {Sheng, Hua and Frei, Heinz},
abstractNote = {In the search for the two-electron-reduced intermediate of the tetraaza catalyst [CoIIN4H(MeCN)]2+ (N4H = 2,12-dimethyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),2,11,13,15-pentaene) for CO2 reduction and elementary steps that result in the formation of CO product, rapid-scan FT-IR spectroscopy of the visible-light-sensitized catalysis, using Ir(ppy)3 in wet acetonitrile (CD3CN) solution, led to the observation of two sequential intermediates. The initially formed one-electron-reduced [CoIN4H]+--CO2 adduct was converted by the second electron to a transient [CoIN4H]+--CO2 - complex that spontaneously converted CO2 to CO in a rate-limiting step on the second time scale in the dark under regeneration of the catalyst (room temperature). The macrocycle IR spectra of the [CoIN4H]+--CO2 - complex and the preceding one-electron [CoIN4H]+--CO2 intermediate show close similarity but distinct differences in the carboxylate modes, indicating that the second electron resides mainly on the CO2 ligand. Vibrational assignments are corroborated by 13C isotopic labeling. The structure and stability of the two-electron-reduced intermediate derived from the time-resolved IR study are in good agreement with recent predictions by DFT electronic structure calculations. This is the first observation of an intermediate of a molecular catalyst for CO2 reduction during the bond-breaking step producing CO. The reaction pathway for the Co tetraaza catalyst uncovered here suggests that the competition between CO2 reduction and proton reduction of a macrocyclic multi-electron catalyst is steered toward CO2 activation if the second electron is directly captured by an adduct of CO2 and the one-electron-reduced catalyst intermediate.},
doi = {10.1021/jacs.6b05248},
journal = {Journal of the American Chemical Society},
number = 31,
volume = 138,
place = {United States},
year = {Fri Jul 15 00:00:00 EDT 2016},
month = {Fri Jul 15 00:00:00 EDT 2016}
}