Hydrogen-Atom Transfer Oxidation with H2O2 Catalyzed by [FeII(1,2-bis(2,2′-bipyridyl-6-yl)ethane(H2O)2]2+

Likely Involvement of a (μ-Hydroxo)(μ-1,2-peroxo)diiron(III) Intermediate

Alexander M. Khenkin, Madhu Vedichi, Linda J.W. Shimon, Matthew A. Cranswick, Johannes E.M.N. Klein, Lawrence Que, Ronny Neumann

Research output: Contribution to journalArticle

Abstract

The iron(II) triflate complex (1) of 1,2-bis(2,2′-bipyridyl-6-yl)ethane, with two bipyridine moieties connected by an ethane bridge, was prepared. Addition of aqueous 30 % H2O2 to an acetonitrile solution of 1 yielded 2, a green compound with λmax=710 nm. Moessbauer measurements on 2 showed a doublet with an isomer shift (δ) of 0.35 mm/s and a quadrupole splitting (ΔEQ) of 0.86 mm/s, indicative of an antiferromagnetically coupled diferric complex. Resonance Raman spectra showed peaks at 883, 556 and 451 cm−1 that downshifted to 832, 540 and 441 cm−1 when 1 was treated with H2 18O2. All the spectroscopic data support the initial formation of a (μ-hydroxo)(μ-1,2-peroxo)diiron(III) complex that oxidizes carbon-hydrogen bonds. At 0 °C 2 reacted with cyclohexene to yield allylic oxidation products but not epoxide. Weak benzylic C−H bonds of alkylarenes were also oxidized. A plot of the logarithms of the second order rate constants versus the bond dissociation energies of the cleaved C−H bond showed an excellent linear correlation. Along with the observation that oxidation of the probe substrate 2,2-dimethyl-1-phenylpropan-1-ol yielded the corresponding ketone but no benzaldehyde, and the kinetic isotope effect, kH/kD, of 2.8 found for the oxidation of xanthene, the results support the hypothesis for a metal-based H-atom abstraction mechanism. Complex 2 is a rare example of a (μ-hydroxo)(μ-1,2-peroxo)diiron(III) complex that can elicit the oxidation of carbon-hydrogen bonds.

Original languageEnglish
Pages (from-to)990-998
Number of pages9
JournalIsrael Journal of Chemistry
Volume57
Issue number10
DOIs
Publication statusPublished - Nov 1 2017

Fingerprint

2,2'-Dipyridyl
Ethane
Hydrogen
Atoms
Oxidation
Hydrogen bonds
Carbon
Xanthenes
Epoxy Compounds
Ketones
Isotopes
Isomers
Raman scattering
Rate constants
Metals
Kinetics
Substrates

Keywords

  • Bridging ligands
  • C−H bond activation
  • hydrogen-atom abstraction
  • O−O bond activation
  • peroxo

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Hydrogen-Atom Transfer Oxidation with H2O2 Catalyzed by [FeII(1,2-bis(2,2′-bipyridyl-6-yl)ethane(H2O)2]2+ : Likely Involvement of a (μ-Hydroxo)(μ-1,2-peroxo)diiron(III) Intermediate. / Khenkin, Alexander M.; Vedichi, Madhu; Shimon, Linda J.W.; Cranswick, Matthew A.; Klein, Johannes E.M.N.; Que, Lawrence; Neumann, Ronny.

In: Israel Journal of Chemistry, Vol. 57, No. 10, 01.11.2017, p. 990-998.

Research output: Contribution to journalArticle

Khenkin, Alexander M. ; Vedichi, Madhu ; Shimon, Linda J.W. ; Cranswick, Matthew A. ; Klein, Johannes E.M.N. ; Que, Lawrence ; Neumann, Ronny. / Hydrogen-Atom Transfer Oxidation with H2O2 Catalyzed by [FeII(1,2-bis(2,2′-bipyridyl-6-yl)ethane(H2O)2]2+ : Likely Involvement of a (μ-Hydroxo)(μ-1,2-peroxo)diiron(III) Intermediate. In: Israel Journal of Chemistry. 2017 ; Vol. 57, No. 10. pp. 990-998.
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T1 - Hydrogen-Atom Transfer Oxidation with H2O2 Catalyzed by [FeII(1,2-bis(2,2′-bipyridyl-6-yl)ethane(H2O)2]2+

T2 - Likely Involvement of a (μ-Hydroxo)(μ-1,2-peroxo)diiron(III) Intermediate

AU - Khenkin, Alexander M.

AU - Vedichi, Madhu

AU - Shimon, Linda J.W.

AU - Cranswick, Matthew A.

AU - Klein, Johannes E.M.N.

AU - Que, Lawrence

AU - Neumann, Ronny

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N2 - The iron(II) triflate complex (1) of 1,2-bis(2,2′-bipyridyl-6-yl)ethane, with two bipyridine moieties connected by an ethane bridge, was prepared. Addition of aqueous 30 % H2O2 to an acetonitrile solution of 1 yielded 2, a green compound with λmax=710 nm. Moessbauer measurements on 2 showed a doublet with an isomer shift (δ) of 0.35 mm/s and a quadrupole splitting (ΔEQ) of 0.86 mm/s, indicative of an antiferromagnetically coupled diferric complex. Resonance Raman spectra showed peaks at 883, 556 and 451 cm−1 that downshifted to 832, 540 and 441 cm−1 when 1 was treated with H2 18O2. All the spectroscopic data support the initial formation of a (μ-hydroxo)(μ-1,2-peroxo)diiron(III) complex that oxidizes carbon-hydrogen bonds. At 0 °C 2 reacted with cyclohexene to yield allylic oxidation products but not epoxide. Weak benzylic C−H bonds of alkylarenes were also oxidized. A plot of the logarithms of the second order rate constants versus the bond dissociation energies of the cleaved C−H bond showed an excellent linear correlation. Along with the observation that oxidation of the probe substrate 2,2-dimethyl-1-phenylpropan-1-ol yielded the corresponding ketone but no benzaldehyde, and the kinetic isotope effect, kH/kD, of 2.8 found for the oxidation of xanthene, the results support the hypothesis for a metal-based H-atom abstraction mechanism. Complex 2 is a rare example of a (μ-hydroxo)(μ-1,2-peroxo)diiron(III) complex that can elicit the oxidation of carbon-hydrogen bonds.

AB - The iron(II) triflate complex (1) of 1,2-bis(2,2′-bipyridyl-6-yl)ethane, with two bipyridine moieties connected by an ethane bridge, was prepared. Addition of aqueous 30 % H2O2 to an acetonitrile solution of 1 yielded 2, a green compound with λmax=710 nm. Moessbauer measurements on 2 showed a doublet with an isomer shift (δ) of 0.35 mm/s and a quadrupole splitting (ΔEQ) of 0.86 mm/s, indicative of an antiferromagnetically coupled diferric complex. Resonance Raman spectra showed peaks at 883, 556 and 451 cm−1 that downshifted to 832, 540 and 441 cm−1 when 1 was treated with H2 18O2. All the spectroscopic data support the initial formation of a (μ-hydroxo)(μ-1,2-peroxo)diiron(III) complex that oxidizes carbon-hydrogen bonds. At 0 °C 2 reacted with cyclohexene to yield allylic oxidation products but not epoxide. Weak benzylic C−H bonds of alkylarenes were also oxidized. A plot of the logarithms of the second order rate constants versus the bond dissociation energies of the cleaved C−H bond showed an excellent linear correlation. Along with the observation that oxidation of the probe substrate 2,2-dimethyl-1-phenylpropan-1-ol yielded the corresponding ketone but no benzaldehyde, and the kinetic isotope effect, kH/kD, of 2.8 found for the oxidation of xanthene, the results support the hypothesis for a metal-based H-atom abstraction mechanism. Complex 2 is a rare example of a (μ-hydroxo)(μ-1,2-peroxo)diiron(III) complex that can elicit the oxidation of carbon-hydrogen bonds.

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KW - hydrogen-atom abstraction

KW - O−O bond activation

KW - peroxo

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