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This content will become publicly available on July 11, 2017

Title: Mechanism of photocatalytic reduction of CO2 by Re(bpy)(CO)3Cl from differences in carbon isotope discrimination

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.more » 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.« 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:
OSTI Identifier:
1331074
Report Number(s):
BNL--113175-2016-JA
Journal ID: ISSN 2155-5435; R&D Project: CO026; KC0304030
Grant/Contract Number:
SC00112704
Type:
Accepted Manuscript
Journal Name:
ACS Catalysis
Additional Journal Information:
Journal Volume: 6; Journal Issue: 8; Journal ID: ISSN 2155-5435
Publisher:
American Chemical Society
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; homogeneous catalysis; isotope effects; isotopic discrimination; photocatalysis