Combined experimental and theoretical approach to understand the reactivity of a mononuclear Cu(II)-hydroperoxo complex in oxygenation reactions

Takashi Kamachi, Yong Min Lee, Tomonori Nishimi, Jaeheung Cho, Kazunari Yoshizawa, Wonwoo Nam

Research output: Contribution to journalArticle

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Abstract

A copper(II) complex bearing a pentadentate ligand, [CuII(N4Py) (CF3SO3)2] (1) (N4Py = N, N-bis(2- pyridylmethyl)bis(2-pyridyl)methylamine), was synthesized and characterized with various spectroscopic techniques and X-ray crystallography. A mononuclear CuII-hydroperoxo complex, [CuII(N4Py)(OOH)]+ (2), was then generated in the reaction of 1 and H2O2 in the presence of base, and the reactivity of the intermediate was investigated in the oxidation of various substrates at -40 °C. In the reactivity studies, 2 showed a low oxidizing power such that 2 reacted only with triethylphosphine but not with other substrates such as thioanisole, benzyl alcohol, 1, 4-cyclohexadiene, cyclohexene, and cyclohexane. In theoretical work, we have conducted density functional theory (DFT) calculations on the epoxidation of ethylene by 2 and a [CuIII(N4Py)(O)]+ intermediate (3) at the B3LYP level. The activation barrier is calculated to be 39.7 and 26.3 kcal/mol for distal and proximal oxygen attacks by 2, respectively. This result indicates that the direct ethylene epoxidation by 2 is not a plausible pathway, as we have observed in the experimental work. In contrast, the ethylene epoxidation by 3 is a downhill and low-barrier process. We also found that 2 cannot be a precursor to 3, since the homolytic cleavage of the O-O bond of 2 is very endothermic (i.e., 42 kcal/mol). On the basis of the experimental and theoretical results, we conclude that a mononuclear CuII-hydroperoxo species bearing a pentadentate N5 ligand is a sluggish oxidant in oxygenation reactions.

Original languageEnglish
Pages (from-to)13102-13108
Number of pages7
JournalJournal of Physical Chemistry A
Volume112
Issue number50
DOIs
Publication statusPublished - Dec 18 2008

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epoxidation
Oxygenation
Epoxidation
oxygenation
Bearings (structural)
ethylene
reactivity
Ligands
Benzyl Alcohol
ligands
X ray crystallography
Substrates
Oxidants
cyclohexane
attack
crystallography
Density functional theory
Copper
cleavage
alcohols

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry

Cite this

Combined experimental and theoretical approach to understand the reactivity of a mononuclear Cu(II)-hydroperoxo complex in oxygenation reactions. / Kamachi, Takashi; Lee, Yong Min; Nishimi, Tomonori; Cho, Jaeheung; Yoshizawa, Kazunari; Nam, Wonwoo.

In: Journal of Physical Chemistry A, Vol. 112, No. 50, 18.12.2008, p. 13102-13108.

Research output: Contribution to journalArticle

Kamachi, Takashi ; Lee, Yong Min ; Nishimi, Tomonori ; Cho, Jaeheung ; Yoshizawa, Kazunari ; Nam, Wonwoo. / Combined experimental and theoretical approach to understand the reactivity of a mononuclear Cu(II)-hydroperoxo complex in oxygenation reactions. In: Journal of Physical Chemistry A. 2008 ; Vol. 112, No. 50. pp. 13102-13108.
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abstract = "A copper(II) complex bearing a pentadentate ligand, [CuII(N4Py) (CF3SO3)2] (1) (N4Py = N, N-bis(2- pyridylmethyl)bis(2-pyridyl)methylamine), was synthesized and characterized with various spectroscopic techniques and X-ray crystallography. A mononuclear CuII-hydroperoxo complex, [CuII(N4Py)(OOH)]+ (2), was then generated in the reaction of 1 and H2O2 in the presence of base, and the reactivity of the intermediate was investigated in the oxidation of various substrates at -40 °C. In the reactivity studies, 2 showed a low oxidizing power such that 2 reacted only with triethylphosphine but not with other substrates such as thioanisole, benzyl alcohol, 1, 4-cyclohexadiene, cyclohexene, and cyclohexane. In theoretical work, we have conducted density functional theory (DFT) calculations on the epoxidation of ethylene by 2 and a [CuIII(N4Py)(O)]+ intermediate (3) at the B3LYP level. The activation barrier is calculated to be 39.7 and 26.3 kcal/mol for distal and proximal oxygen attacks by 2, respectively. This result indicates that the direct ethylene epoxidation by 2 is not a plausible pathway, as we have observed in the experimental work. In contrast, the ethylene epoxidation by 3 is a downhill and low-barrier process. We also found that 2 cannot be a precursor to 3, since the homolytic cleavage of the O-O bond of 2 is very endothermic (i.e., 42 kcal/mol). On the basis of the experimental and theoretical results, we conclude that a mononuclear CuII-hydroperoxo species bearing a pentadentate N5 ligand is a sluggish oxidant in oxygenation reactions.",
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AU - Kamachi, Takashi

AU - Lee, Yong Min

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AU - Nam, Wonwoo

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