title: Selectivity and Mechanism of Hydrogen Atom Transfer by an Isolable
 Imidoiron (III) Complex
creator: Cowley, Ryan E.
creator: Eckert, Nathan A.
creator: Vaddadi, Sridhar
creator: Figg, Travis M.
creator: Cundari, Thomas R., 1964-
creator: Holland, Patrick L.
publisher: American Chemical Society
date: 2011-05-12
language: English
description: This article discusses the selectivity and mechanism of hydrogen
 atom transfer by an isolable imidoiron (III) complex. In the literature,
 iron-oxo complexes have been isolated and their hydrogen atom transfer (HAT)
 reactions have been studied in detail. Iron-imido complexes have been isolated
 more recently, and the community needs experimental evaluations of the
 mechanism of HAT from late-metal imido species. The authors report a
 mechanistic study of HAT by an isolable iron (III) imido complex, LᴹᵉFeNAd
 (Lᴹᵉ = bulky β-diketiminate ligand, 2,4-bis(2,6-diisopropylphenylimido)pentyl;
 Ad = 1-adamantyl). HAT is preceded by binding of tert-butylpyridine (ᵗBupy) to
 form a reactive four-coordinate intermediate LᴹᵉFe(NAd)(ᵗBupy), as shown by
 equilibrium and kinetic studies. In the HAT step, very large substrate H/D
 kinetic isotope effects around 100 are consistent with C-H bond cleavage. The
 elementary HAT rate constant is increased by electron-donating groups on the
 pyridine additive, and by a more polar medium. When combined with the faster
 rate of HAT from indene versus cyclohexadiene, this trend is consistent with
 H⁺ transfer character in the HAT transition state. The increase in HAT rate in
 the presence of ᵗBupy may be explained by a combination of electronic (weaker
 Fe=N π-bonding) and thermodynamic (more exothermic HAT) effects. Most
 importantly, HAT by these imido complexes has a strong dependence on the size
 of the hydrocarbon substrate. This selectivity comes from steric hindrance by
 the spectator ligands, a strategy that has promise for controlling the
 regioselectivity of these C-H bond activation reactions.
subject: hydrogen atom transfers
subject: iron-imido complexes
subject: kinetic isotopes
subject: ligands
source: Journal of the American Chemical Society, 2011, Washington DC: American
 Chemical Society, pp. 9796-9811
rights: Public
type: Article
format: 16 p.
format: Text
identifier: doi: 10.1021/ja2005303
identifier: http://digital.library.unt.edu/ark:/67531/metadc107786/
identifier: ark: ark:/67531/metadc107786