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Engineering the Oxidative Potency of Non-Heme Iron(IV) Oxo Complexes in Water for C-H Oxidation by a cis Donor and Variation of the Second Coordination Sphere

Wegeberg, Christina ; Skavenborg, Mathias L. ; Liberato, Andrea ; McPherson, James N. ; Browne, Wesley R. ; Hedegård, Erik D. LU and McKenzie, Christine J. (2021) In Inorganic Chemistry 60(3). p.1975-1984
Abstract

A series of iron(IV) oxo complexes, which differ in the donor (CH2py or CH2COO-) cis to the oxo group, three with hemilabile pendant donor/second coordination sphere base/acid arms (pyH/py or ROH), have been prepared in water at pH 2 and 7. The νFe=O values of 832 ± 2 cm-1 indicate similar FeIV=O bond strengths; however, different reactivities toward C-H substrates in water are observed. HAT occurs at rates that differ by 1 order of magnitude with nonclassical KIEs (kH/kD = 30-66) consistent with hydrogen atom tunneling. Higher KIEs correlate with faster reaction rates as well as a greater thermodynamic stability of the iron(III) resting states. A doubling in rate from pH 7 to pH 2 for substrate C-H oxidation by the most potent complex,... (More)

A series of iron(IV) oxo complexes, which differ in the donor (CH2py or CH2COO-) cis to the oxo group, three with hemilabile pendant donor/second coordination sphere base/acid arms (pyH/py or ROH), have been prepared in water at pH 2 and 7. The νFe=O values of 832 ± 2 cm-1 indicate similar FeIV=O bond strengths; however, different reactivities toward C-H substrates in water are observed. HAT occurs at rates that differ by 1 order of magnitude with nonclassical KIEs (kH/kD = 30-66) consistent with hydrogen atom tunneling. Higher KIEs correlate with faster reaction rates as well as a greater thermodynamic stability of the iron(III) resting states. A doubling in rate from pH 7 to pH 2 for substrate C-H oxidation by the most potent complex, that with a cis-carboxylate donor, [FeIVO(Htpena)]2+, is observed. Supramolecular assistance by the first and second coordination spheres in activating the substrate is proposed. The lifetime of this complex in the absence of a C-H substrate is the shortest (at pH 2, 3 h vs up to 1.3 days for the most stable complex), implying that slow water oxidation is a competing background reaction. The iron(IV)=O complex bearing an alcohol moiety in the second coordination sphere displays significantly shorter lifetimes due to a competing selective intramolecular oxidation of the ligand.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Inorganic Chemistry
volume
60
issue
3
pages
1975 - 1984
publisher
The American Chemical Society (ACS)
external identifiers
  • scopus:85100266929
  • pmid:33470794
ISSN
0020-1669
DOI
10.1021/acs.inorgchem.0c03441
language
English
LU publication?
yes
id
6a457ebf-da42-45b0-a36a-ab1b3dc0485d
date added to LUP
2021-02-15 09:58:28
date last changed
2022-11-16 05:25:58
@article{6a457ebf-da42-45b0-a36a-ab1b3dc0485d,
  abstract     = {{<p>A series of iron(IV) oxo complexes, which differ in the donor (CH2py or CH2COO-) cis to the oxo group, three with hemilabile pendant donor/second coordination sphere base/acid arms (pyH/py or ROH), have been prepared in water at pH 2 and 7. The νFe=O values of 832 ± 2 cm-1 indicate similar FeIV=O bond strengths; however, different reactivities toward C-H substrates in water are observed. HAT occurs at rates that differ by 1 order of magnitude with nonclassical KIEs (kH/kD = 30-66) consistent with hydrogen atom tunneling. Higher KIEs correlate with faster reaction rates as well as a greater thermodynamic stability of the iron(III) resting states. A doubling in rate from pH 7 to pH 2 for substrate C-H oxidation by the most potent complex, that with a cis-carboxylate donor, [FeIVO(Htpena)]2+, is observed. Supramolecular assistance by the first and second coordination spheres in activating the substrate is proposed. The lifetime of this complex in the absence of a C-H substrate is the shortest (at pH 2, 3 h vs up to 1.3 days for the most stable complex), implying that slow water oxidation is a competing background reaction. The iron(IV)=O complex bearing an alcohol moiety in the second coordination sphere displays significantly shorter lifetimes due to a competing selective intramolecular oxidation of the ligand. </p>}},
  author       = {{Wegeberg, Christina and Skavenborg, Mathias L. and Liberato, Andrea and McPherson, James N. and Browne, Wesley R. and Hedegård, Erik D. and McKenzie, Christine J.}},
  issn         = {{0020-1669}},
  language     = {{eng}},
  number       = {{3}},
  pages        = {{1975--1984}},
  publisher    = {{The American Chemical Society (ACS)}},
  series       = {{Inorganic Chemistry}},
  title        = {{Engineering the Oxidative Potency of Non-Heme Iron(IV) Oxo Complexes in Water for C-H Oxidation by a cis Donor and Variation of the Second Coordination Sphere}},
  url          = {{http://dx.doi.org/10.1021/acs.inorgchem.0c03441}},
  doi          = {{10.1021/acs.inorgchem.0c03441}},
  volume       = {{60}},
  year         = {{2021}},
}