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Mechanistic Insights into the C-H Bond Activation of Hydrocarbons by Chromium(IV) Oxo and Chromium(III) Superoxo Complexes

Mechanistic Insights into the C-H Bond Activation of Hydrocarbons by Chromium(IV) Oxo and Chromium(III) Superoxo Complexes
Cho, KB[Cho, Kyung-Bin]Kang, H[Kang, Hyeona]Woo, J[Woo, Jaeyoung]Park, YJ[Park, Young Jun]Seo, MS[Seo, Mi Sook]Cho, J[Cho, Jaeheung]Nam, W[Nam, Wonwoo]
DGIST Authors
Cho, J[Cho, Jaeheung]
Issue Date
Inorganic Chemistry, 53(1), 645-652
Article Type
Chemical StructureChemistryChromiumConformationCrystallography, X-RayHydrocarbonHydrocarbonsModels, MolecularMolecular ConformationOrganometallic CompoundOrganometallic CompoundsOxygenQuantum TheoryX Ray Crystallography
The mechanism of the C-H bond activation of hydrocarbons by a nonheme chromium(IV) oxo complex bearing an N-methylated tetraazamacrocyclic cyclam (TMC) ligand, [CrIV(O)(TMC)(Cl)]+ (2), has been investigated experimentally and theoretically. In experimental studies, reaction rates of 2 with substrates having weak C-H bonds were found to depend on the concentration and bond dissociation energies of the substrates. A large kinetic isotope effect value of 60 was determined in the oxidation of dihydroanthracene (DHA) and deuterated DHA by 2. These results led us to propose that the C-H bond activation reaction occurs via a H-atom abstraction mechanism, in which H-atom abstraction of substrates by 2 is the rate-determining step. In addition, formation of a chromium(III) hydroxo complex, [CrIII(OH)(TMC)(Cl)] + (3), was observed as a decomposed product of 2 in the C-H bond activation reaction. The CrIIIOH product was characterized unambiguously with various spectroscopic methods and X-ray crystallography. Density functional theory (DFT) calculations support the experimental observations that the C-H bond activation by 2 does not occur via the conventional H-atom-abstraction/oxygen-rebound mechanism and that 3 is the product formed in this C-H bond activation reaction. DFT calculations also propose that 2 may have some CrIIIO•- character. The oxidizing power of 2 was then compared with that of a chromium(III) superoxo complex bearing the identical TMC ligand, [CrIII(O 2)(TMC)(Cl)]+ (1), in the C-H bond activation reaction. By performing reactions of 1 and 2 with substrates under identical conditions, we were able to demonstrate that the reactivity of 2 is slightly greater than that of 1. DFT calculations again support this experimental observation, showing that the rate-limiting barrier for the reaction with 2 is slightly lower than that of 1. © 2013 American Chemical Society.
American Chemical Society
Related Researcher
  • Author Cho, Jaeheung Biomimetic Materials Laboratory
  • Research Interests Biomimetics; Metalloenzymes; Nitric Oxide Suppliers in Brain; Biomimetic Materials in Life
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Department of Emerging Materials ScienceBiomimetic Materials Laboratory1. Journal Articles

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