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Mechanism Insights of Ethane C-H Bond Activations by Bare [Fe-III=O](+): Explicit Electronic Structure Analysis

Sun, Xiao-Li; Huang, Xu-Ri; Li, Jilai LU ; Huo, Rui-Ping and Sun, Chia-Chung (2012) In The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory 116(5). p.1475-1485
Abstract
Alkane C-H bond activation by various catalysts and enzymes has attracted considerable attention recently, but many issues are still unanswered. The conversion of ethane to ethanol and ethene by bare [Fe-III=O](+) has been explored using density functional theory and coupled-cluster method comprehensively. Two possible reaction mechanisms are available for the entire reaction, the direct H-abstraction mechanism and the concerted mechanism. First, in the direct H-abstraction mechanism, a direct H-abstraction is encountered in the initial step, going through a collinear transition state C center dot center dot center dot H center dot center dot center dot O-Fe and then leading to the generation of an intermediate Fe-OH bound to the alkyl... (More)
Alkane C-H bond activation by various catalysts and enzymes has attracted considerable attention recently, but many issues are still unanswered. The conversion of ethane to ethanol and ethene by bare [Fe-III=O](+) has been explored using density functional theory and coupled-cluster method comprehensively. Two possible reaction mechanisms are available for the entire reaction, the direct H-abstraction mechanism and the concerted mechanism. First, in the direct H-abstraction mechanism, a direct H-abstraction is encountered in the initial step, going through a collinear transition state C center dot center dot center dot H center dot center dot center dot O-Fe and then leading to the generation of an intermediate Fe-OH bound to the alkyl radical weakly. The final product of the direct H-abstraction mechanism is ethanol, which is produced by the hydroxyl group back transfer to the carbon radical. Second, in the concerted reaction mechanism, the H-abstraction process is characterized via overcoming four/five-centered transition states (TSH)-T-6/4_c5 or (TSH)-T-4_c4. The second step of the concerted mechanism can lead to either product ethanol or ethene. Moreover, the major product ethene can be obtained through two different pathways, the one-step pathway and the stepwise pathway. It is the first report that the former pathway starting from (IM)-I-6/4_c to the product can be better described as a proton-coupled electron transfer (PCET). It plays an important role in the product ethene generation according to the CCSD(T) results. The spin-orbital coupling (SOC) calculations demonstrate that the title reaction should proceed via a two-state reactivity (TSR) pattern and that the spin-forbidden transition could slightly lower the rate-determining energy barrier height. This thorough theoretical study, especially the explicit electronic structure analysis, may provide important clues for understanding and studying the C-H bond activation promoted by iron-based artificial catalysts. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory
volume
116
issue
5
pages
1475 - 1485
publisher
The American Chemical Society
external identifiers
  • wos:000299985100018
  • scopus:84863161798
ISSN
1520-5215
DOI
10.1021/jp2120302
language
English
LU publication?
yes
id
8f8f4c6b-5647-4214-a83b-270b14b2b6d7 (old id 2409806)
date added to LUP
2012-03-28 11:14:45
date last changed
2017-09-17 06:42:17
@article{8f8f4c6b-5647-4214-a83b-270b14b2b6d7,
  abstract     = {Alkane C-H bond activation by various catalysts and enzymes has attracted considerable attention recently, but many issues are still unanswered. The conversion of ethane to ethanol and ethene by bare [Fe-III=O](+) has been explored using density functional theory and coupled-cluster method comprehensively. Two possible reaction mechanisms are available for the entire reaction, the direct H-abstraction mechanism and the concerted mechanism. First, in the direct H-abstraction mechanism, a direct H-abstraction is encountered in the initial step, going through a collinear transition state C center dot center dot center dot H center dot center dot center dot O-Fe and then leading to the generation of an intermediate Fe-OH bound to the alkyl radical weakly. The final product of the direct H-abstraction mechanism is ethanol, which is produced by the hydroxyl group back transfer to the carbon radical. Second, in the concerted reaction mechanism, the H-abstraction process is characterized via overcoming four/five-centered transition states (TSH)-T-6/4_c5 or (TSH)-T-4_c4. The second step of the concerted mechanism can lead to either product ethanol or ethene. Moreover, the major product ethene can be obtained through two different pathways, the one-step pathway and the stepwise pathway. It is the first report that the former pathway starting from (IM)-I-6/4_c to the product can be better described as a proton-coupled electron transfer (PCET). It plays an important role in the product ethene generation according to the CCSD(T) results. The spin-orbital coupling (SOC) calculations demonstrate that the title reaction should proceed via a two-state reactivity (TSR) pattern and that the spin-forbidden transition could slightly lower the rate-determining energy barrier height. This thorough theoretical study, especially the explicit electronic structure analysis, may provide important clues for understanding and studying the C-H bond activation promoted by iron-based artificial catalysts.},
  author       = {Sun, Xiao-Li and Huang, Xu-Ri and Li, Jilai and Huo, Rui-Ping and Sun, Chia-Chung},
  issn         = {1520-5215},
  language     = {eng},
  number       = {5},
  pages        = {1475--1485},
  publisher    = {The American Chemical Society},
  series       = {The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory},
  title        = {Mechanism Insights of Ethane C-H Bond Activations by Bare [Fe-III=O](+): Explicit Electronic Structure Analysis},
  url          = {http://dx.doi.org/10.1021/jp2120302},
  volume       = {116},
  year         = {2012},
}