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Catalytic C-H oxidations by nonheme mononuclear Fe(II) complexes of two pentadentate ligands: Evidence for an Fe(IV) oxo intermediate

Mitra, Mainak LU ; Nimir, Hassan; Hrovat, David A.; Shteinman, Albert A.; Richmond, Michael G.; Costas, Miquel and Nordlander, Ebbe LU (2017) In Journal of Molecular Catalysis A: Chemical 426. p.350-356
Abstract
The oxidation reactions of alkanes with hydrogen peroxide and peracids (peracetic acid (PAA) and m-chloroperoxybenzoic acid (mCPBA)) catalysed by two Fe(II) complexes of pentadentate {N5}-donor ligands have been investigated. Kinetic isotope effect experiments and the use of other mechanistic probes have also been performed. While the total yields of oxidized products are similar regardless of oxidant (e.g. 30–39% for oxidation of cyclohexane), the observed alcohol/ketone ratios and kinetic isotope effects differ significantly with different oxidants. Catalytic reactions in H2O2 medium are consistent with the involvement of hydroxyl radicals in the Csingle bondH bond cleavage step, and resultant low kinetic isotope effect values. On the... (More)
The oxidation reactions of alkanes with hydrogen peroxide and peracids (peracetic acid (PAA) and m-chloroperoxybenzoic acid (mCPBA)) catalysed by two Fe(II) complexes of pentadentate {N5}-donor ligands have been investigated. Kinetic isotope effect experiments and the use of other mechanistic probes have also been performed. While the total yields of oxidized products are similar regardless of oxidant (e.g. 30–39% for oxidation of cyclohexane), the observed alcohol/ketone ratios and kinetic isotope effects differ significantly with different oxidants. Catalytic reactions in H2O2 medium are consistent with the involvement of hydroxyl radicals in the Csingle bondH bond cleavage step, and resultant low kinetic isotope effect values. On the other hand, catalytic reactions performed using peracid media indicate the involvement of an oxidant different from the hydroxyl radical. For these reactions, the kinetic isotope effect values are relatively high (within a range of 4.2–5.1) and the C3/C2 selectivity parameters in adamantane oxidation are greater than 11, thereby excluding the presence of hydroxyl radicals in the Csingle bondH bond cleavage step. A low spin Fe(III)-OOH species has been detected in the H2O2-based catalytic system by UV/Vis, mass spectrometry and EPR spectroscopy, while an Fe(IV)-oxo species is postulated to be the active oxidant in the peracid-based catalytic systems. Computational studies on the Csingle bondH oxidation mechanism reveal that while the hydroxyl radical is mainly responsible for the H-atom abstraction in the H2O2-based catalytic system, it is the Fe(IV)-oxo species that abstracts the H-atom from the substrate in the peracid-based catalytic systems, in agreement with the experimental observations. (Less)
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Contribution to journal
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published
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in
Journal of Molecular Catalysis A: Chemical
volume
426
pages
7 pages
publisher
Elsevier
external identifiers
  • scopus:85003486059
  • wos:000391075700009
ISSN
1381-1169
DOI
10.1016/j.molcata.2016.10.010
language
English
LU publication?
yes
id
aed84a48-6586-4e46-bad9-a661fb6c381e
date added to LUP
2016-12-16 09:06:44
date last changed
2018-01-07 11:41:13
@article{aed84a48-6586-4e46-bad9-a661fb6c381e,
  abstract     = {The oxidation reactions of alkanes with hydrogen peroxide and peracids (peracetic acid (PAA) and m-chloroperoxybenzoic acid (mCPBA)) catalysed by two Fe(II) complexes of pentadentate {N5}-donor ligands have been investigated. Kinetic isotope effect experiments and the use of other mechanistic probes have also been performed. While the total yields of oxidized products are similar regardless of oxidant (e.g. 30–39% for oxidation of cyclohexane), the observed alcohol/ketone ratios and kinetic isotope effects differ significantly with different oxidants. Catalytic reactions in H2O2 medium are consistent with the involvement of hydroxyl radicals in the Csingle bondH bond cleavage step, and resultant low kinetic isotope effect values. On the other hand, catalytic reactions performed using peracid media indicate the involvement of an oxidant different from the hydroxyl radical. For these reactions, the kinetic isotope effect values are relatively high (within a range of 4.2–5.1) and the C3/C2 selectivity parameters in adamantane oxidation are greater than 11, thereby excluding the presence of hydroxyl radicals in the Csingle bondH bond cleavage step. A low spin Fe(III)-OOH species has been detected in the H2O2-based catalytic system by UV/Vis, mass spectrometry and EPR spectroscopy, while an Fe(IV)-oxo species is postulated to be the active oxidant in the peracid-based catalytic systems. Computational studies on the Csingle bondH oxidation mechanism reveal that while the hydroxyl radical is mainly responsible for the H-atom abstraction in the H2O2-based catalytic system, it is the Fe(IV)-oxo species that abstracts the H-atom from the substrate in the peracid-based catalytic systems, in agreement with the experimental observations.},
  author       = {Mitra, Mainak and Nimir, Hassan and Hrovat, David A. and Shteinman, Albert A. and Richmond, Michael G. and Costas, Miquel and Nordlander, Ebbe},
  issn         = {1381-1169},
  language     = {eng},
  pages        = {350--356},
  publisher    = {Elsevier},
  series       = {Journal of Molecular Catalysis A: Chemical},
  title        = {Catalytic C-H oxidations by nonheme mononuclear Fe(II) complexes of two pentadentate ligands: Evidence for an Fe(IV) oxo intermediate},
  url          = {http://dx.doi.org/10.1016/j.molcata.2016.10.010},
  volume       = {426},
  year         = {2017},
}