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Title: Mechanism of photocatalytic reduction of CO 2 by Re(bpy)(CO) 3Cl from differences in carbon isotope discrimination

Abstract

The rhenium complex Re(bpy)(CO) 3Cl (1, bpy = 2,2'-bipyridine) catalyzes CO 2 reduction to CO in mixtures containing triethanolamine (TEOA) as a sacrificial reductant. The mechanism of this reaction under photocatalytic conditions remains to be fully characterized. Here, we report the competitive carbon kinetic isotope effects ( 13C KIEs) on photocatalytic CO 2 reduction by 1 and analyze the results of experimental measurements by comparing with computed KIEs via density functional theory (DFT) calculations as a means of formulating a chemical mechanism and illustrating the utility of this approach. The 13C KIEs, k( 12C)/k( 13C), in acetonitrile (ACN) and dimethylformamide (DMF) were determined to be 1.0718 ± 0.0036 and 1.0685 ± 0.0075, respectively. When [Ru(bpy) 3]Cl 2 is added to the reaction mixture in acetonitrile as a photosensitizer, the reduction of CO 2 exhibited a 13C KIE = 1.0703 ± 0.0043. These values are consistent with the calculated isotope effect of CO 2 binding to the one-electron reduced [ReI(bpy• )(CO) 3] species. The findings reported here provide strong evidence that the reactions in the two different solvents have the same first irreversible step and proceed with similar reactive intermediates upon reduction. Theoretically, we found that the major contribution for themore » large 13C isotope effects comes from a dominant zero-point energy (ZPE) term. Lastly, these results lay the groundwork for combined experimental and theoretical approaches for analysis of competitive isotope effects toward understanding CO 2 reduction catalyzed by other complexes.« less

Authors:
 [1];  [2];  [2];  [1]
  1. Univ. of Connecticut, Storrs, CT (United States)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States)
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1331074
Report Number(s):
BNL-113175-2016-JA
Journal ID: ISSN 2155-5435; R&D Project: CO026; KC0304030
Grant/Contract Number:  
SC00112704
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
ACS Catalysis
Additional Journal Information:
Journal Volume: 6; Journal Issue: 8; Journal ID: ISSN 2155-5435
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Schneider, Taylor W., Ertem, Mehmed Z., Muckerman, James T., and Angeles-Boza, Alfredo M. Mechanism of photocatalytic reduction of CO2 by Re(bpy)(CO)3Cl from differences in carbon isotope discrimination. United States: N. p., 2016. Web. doi:10.1021/acscatal.6b01208.
Schneider, Taylor W., Ertem, Mehmed Z., Muckerman, James T., & Angeles-Boza, Alfredo M. Mechanism of photocatalytic reduction of CO2 by Re(bpy)(CO)3Cl from differences in carbon isotope discrimination. United States. doi:10.1021/acscatal.6b01208.
Schneider, Taylor W., Ertem, Mehmed Z., Muckerman, James T., and Angeles-Boza, Alfredo M. Mon . "Mechanism of photocatalytic reduction of CO2 by Re(bpy)(CO)3Cl from differences in carbon isotope discrimination". United States. doi:10.1021/acscatal.6b01208. https://www.osti.gov/servlets/purl/1331074.
@article{osti_1331074,
title = {Mechanism of photocatalytic reduction of CO2 by Re(bpy)(CO)3Cl from differences in carbon isotope discrimination},
author = {Schneider, Taylor W. and Ertem, Mehmed Z. and Muckerman, James T. and Angeles-Boza, Alfredo M.},
abstractNote = {The rhenium complex Re(bpy)(CO)3Cl (1, bpy = 2,2'-bipyridine) catalyzes CO2 reduction to CO in mixtures containing triethanolamine (TEOA) as a sacrificial reductant. The mechanism of this reaction under photocatalytic conditions remains to be fully characterized. Here, we report the competitive carbon kinetic isotope effects (13C KIEs) on photocatalytic CO2 reduction by 1 and analyze the results of experimental measurements by comparing with computed KIEs via density functional theory (DFT) calculations as a means of formulating a chemical mechanism and illustrating the utility of this approach. The 13C KIEs, k(12C)/k(13C), in acetonitrile (ACN) and dimethylformamide (DMF) were determined to be 1.0718 ± 0.0036 and 1.0685 ± 0.0075, respectively. When [Ru(bpy)3]Cl2 is added to the reaction mixture in acetonitrile as a photosensitizer, the reduction of CO2 exhibited a 13C KIE = 1.0703 ± 0.0043. These values are consistent with the calculated isotope effect of CO2 binding to the one-electron reduced [ReI(bpy•–)(CO)3] species. The findings reported here provide strong evidence that the reactions in the two different solvents have the same first irreversible step and proceed with similar reactive intermediates upon reduction. Theoretically, we found that the major contribution for the large 13C isotope effects comes from a dominant zero-point energy (ZPE) term. Lastly, these results lay the groundwork for combined experimental and theoretical approaches for analysis of competitive isotope effects toward understanding CO2 reduction catalyzed by other complexes.},
doi = {10.1021/acscatal.6b01208},
journal = {ACS Catalysis},
number = 8,
volume = 6,
place = {United States},
year = {Mon Aug 01 00:00:00 EDT 2016},
month = {Mon Aug 01 00:00:00 EDT 2016}
}

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