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Relationship between Hydrogen-Atom Transfer Driving Force and Reaction Rates for an Oxomanganese(IV) Adduct

Massie, Allyssa A.; Sinha, Arup LU ; Parham, Joshua D.; Nordlander, Ebbe LU and Jackson, Timothy A. (2018) In Inorganic Chemistry 57(14). p.8253-8263
Abstract

Hydrogen atom transfer (HAT) reactions by high-valent metal-oxo intermediates are important in both biological and synthetic systems. While the HAT reactivity of FeIV-oxo adducts has been extensively investigated, studies of analogous MnIV-oxo systems are less common. There are several recent reports of MnIV-oxo complexes, supported by neutral pentadentate ligands, capable of cleaving strong C-H bonds at rates approaching those of analogous FeIV-oxo species. In this study, we provide a thorough analysis of the HAT reactivity of one of these MnIV-oxo complexes, [MnIV(O)(2pyN2Q)]2+, which is supported by an N5 ligand with equatorial pyridine and quinoline donors.... (More)

Hydrogen atom transfer (HAT) reactions by high-valent metal-oxo intermediates are important in both biological and synthetic systems. While the HAT reactivity of FeIV-oxo adducts has been extensively investigated, studies of analogous MnIV-oxo systems are less common. There are several recent reports of MnIV-oxo complexes, supported by neutral pentadentate ligands, capable of cleaving strong C-H bonds at rates approaching those of analogous FeIV-oxo species. In this study, we provide a thorough analysis of the HAT reactivity of one of these MnIV-oxo complexes, [MnIV(O)(2pyN2Q)]2+, which is supported by an N5 ligand with equatorial pyridine and quinoline donors. This complex is able to oxidize the strong C-H bonds of cyclohexane with rates exceeding those of FeIV-oxo complexes with similar ligands. In the presence of excess oxidant (iodosobenzene), cyclohexane oxidation by [MnIV(O)(2pyN2Q)]2+ is catalytic, albeit with modest turnover numbers. Because the rate of cyclohexane oxidation by [MnIV(O)(2pyN2Q)]2+ was faster than that predicted by a previously published Bells-Evans-Polanyi correlation, we expanded the scope of this relationship by determining HAT reaction rates for substrates with bond dissociation energies spanning 20 kcal/mol. This extensive analysis showed the expected correlation between reaction rate and the strength of the substrate C-H bond, albeit with a shallow slope. The implications of this result with regard to MnIV-oxo and FeIV-oxo reactivity are discussed.

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organization
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type
Contribution to journal
publication status
published
subject
in
Inorganic Chemistry
volume
57
issue
14
pages
11 pages
publisher
The American Chemical Society
external identifiers
  • scopus:85049936152
ISSN
0020-1669
DOI
10.1021/acs.inorgchem.8b00852
language
English
LU publication?
yes
id
374008c5-99b2-4aee-936d-1e1d8d7c9da2
date added to LUP
2018-08-01 10:43:29
date last changed
2019-03-19 03:57:53
@article{374008c5-99b2-4aee-936d-1e1d8d7c9da2,
  abstract     = {<p>Hydrogen atom transfer (HAT) reactions by high-valent metal-oxo intermediates are important in both biological and synthetic systems. While the HAT reactivity of Fe<sup>IV</sup>-oxo adducts has been extensively investigated, studies of analogous Mn<sup>IV</sup>-oxo systems are less common. There are several recent reports of Mn<sup>IV</sup>-oxo complexes, supported by neutral pentadentate ligands, capable of cleaving strong C-H bonds at rates approaching those of analogous Fe<sup>IV</sup>-oxo species. In this study, we provide a thorough analysis of the HAT reactivity of one of these Mn<sup>IV</sup>-oxo complexes, [Mn<sup>IV</sup>(O)(2pyN2Q)]<sup>2+</sup>, which is supported by an N5 ligand with equatorial pyridine and quinoline donors. This complex is able to oxidize the strong C-H bonds of cyclohexane with rates exceeding those of Fe<sup>IV</sup>-oxo complexes with similar ligands. In the presence of excess oxidant (iodosobenzene), cyclohexane oxidation by [Mn<sup>IV</sup>(O)(2pyN2Q)]<sup>2+</sup> is catalytic, albeit with modest turnover numbers. Because the rate of cyclohexane oxidation by [Mn<sup>IV</sup>(O)(2pyN2Q)]<sup>2+</sup> was faster than that predicted by a previously published Bells-Evans-Polanyi correlation, we expanded the scope of this relationship by determining HAT reaction rates for substrates with bond dissociation energies spanning 20 kcal/mol. This extensive analysis showed the expected correlation between reaction rate and the strength of the substrate C-H bond, albeit with a shallow slope. The implications of this result with regard to Mn<sup>IV</sup>-oxo and Fe<sup>IV</sup>-oxo reactivity are discussed.</p>},
  author       = {Massie, Allyssa A. and Sinha, Arup and Parham, Joshua D. and Nordlander, Ebbe and Jackson, Timothy A.},
  issn         = {0020-1669},
  language     = {eng},
  month        = {07},
  number       = {14},
  pages        = {8253--8263},
  publisher    = {The American Chemical Society},
  series       = {Inorganic Chemistry},
  title        = {Relationship between Hydrogen-Atom Transfer Driving Force and Reaction Rates for an Oxomanganese(IV) Adduct},
  url          = {http://dx.doi.org/10.1021/acs.inorgchem.8b00852},
  volume       = {57},
  year         = {2018},
}