Cleavage of sp3 C-O bonds via oxidative addition of C-H bonds

Jongwook Choi, Yuriy Choliy, Xiawei Zhang, Thomas J. Emge, Karsten Krogh-Jespersen, Alan S Goldman

Research output: Contribution to journalArticle

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Abstract

(Chemical Equation Presented) (PCP)Ir (PCP = K3-C 6H3-2,6-[CH2P(t-Bu) 2]2) is found to undergo oxidative addition of the methyl-oxygen bond of electron-poor methyl aryl ethers, including methoxy-3,5-bis(trifluoromethyl)benzene and methoxypentafluorobenzene, to give the corresponding aryloxide complexes (PCP)Ir(CH3)(OAr). Although the net reaction is insertion of the Ir center into the C-O bond, density functional theory (DFT) calculations and a significant kinetic isotope effect [kCH3OAr/kCD3OAr = 4.3(3)] strongly argue against a simple insertion mechanism and in favor of a pathway involving C-H addition and ;-migration of the OAr group to give a methylene complex followed by hydride-to-methylene migration to give the observed product. Ethoxy aryl ethers, including ethoxybenzene, also undergo C-O bond cleavage by (PCP)Ir, but the net reaction in this case is 1,2-elimination of ArO-H to give (PCP)Ir(H)(OAr) and ethylene. DFT calculations point to a low-barrier pathway for this reaction that proceeds through C-H addition of the ethoxy methyl group followed by ß-aryl oxide elimination and loss of ethylene. Thus, both of these distinct C-O cleavage reactions proceed via initial addition of a C(sp 3)-H bond, despite the fact that such bonds are typically considered inert and are much stronger than C-O bonds.

Original languageEnglish
Pages (from-to)15627-15629
Number of pages3
JournalJournal of the American Chemical Society
Volume131
Issue number43
DOIs
Publication statusPublished - Nov 4 2009

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Ethers
Density functional theory
Ethylene
Methyl Ethers
Benzene
Hydrides
Isotopes
Oxides
Electrons
Oxygen
Kinetics
ethylene
phenetole

ASJC Scopus subject areas

  • Chemistry(all)
  • Catalysis
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Cleavage of sp3 C-O bonds via oxidative addition of C-H bonds. / Choi, Jongwook; Choliy, Yuriy; Zhang, Xiawei; Emge, Thomas J.; Krogh-Jespersen, Karsten; Goldman, Alan S.

In: Journal of the American Chemical Society, Vol. 131, No. 43, 04.11.2009, p. 15627-15629.

Research output: Contribution to journalArticle

Choi, J, Choliy, Y, Zhang, X, Emge, TJ, Krogh-Jespersen, K & Goldman, AS 2009, 'Cleavage of sp3 C-O bonds via oxidative addition of C-H bonds', Journal of the American Chemical Society, vol. 131, no. 43, pp. 15627-15629. https://doi.org/10.1021/ja906930u
Choi, Jongwook ; Choliy, Yuriy ; Zhang, Xiawei ; Emge, Thomas J. ; Krogh-Jespersen, Karsten ; Goldman, Alan S. / Cleavage of sp3 C-O bonds via oxidative addition of C-H bonds. In: Journal of the American Chemical Society. 2009 ; Vol. 131, No. 43. pp. 15627-15629.
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abstract = "(Chemical Equation Presented) (PCP)Ir (PCP = K3-C 6H3-2,6-[CH2P(t-Bu) 2]2) is found to undergo oxidative addition of the methyl-oxygen bond of electron-poor methyl aryl ethers, including methoxy-3,5-bis(trifluoromethyl)benzene and methoxypentafluorobenzene, to give the corresponding aryloxide complexes (PCP)Ir(CH3)(OAr). Although the net reaction is insertion of the Ir center into the C-O bond, density functional theory (DFT) calculations and a significant kinetic isotope effect [kCH3OAr/kCD3OAr = 4.3(3)] strongly argue against a simple insertion mechanism and in favor of a pathway involving C-H addition and ;-migration of the OAr group to give a methylene complex followed by hydride-to-methylene migration to give the observed product. Ethoxy aryl ethers, including ethoxybenzene, also undergo C-O bond cleavage by (PCP)Ir, but the net reaction in this case is 1,2-elimination of ArO-H to give (PCP)Ir(H)(OAr) and ethylene. DFT calculations point to a low-barrier pathway for this reaction that proceeds through C-H addition of the ethoxy methyl group followed by {\ss}-aryl oxide elimination and loss of ethylene. Thus, both of these distinct C-O cleavage reactions proceed via initial addition of a C(sp 3)-H bond, despite the fact that such bonds are typically considered inert and are much stronger than C-O bonds.",
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AB - (Chemical Equation Presented) (PCP)Ir (PCP = K3-C 6H3-2,6-[CH2P(t-Bu) 2]2) is found to undergo oxidative addition of the methyl-oxygen bond of electron-poor methyl aryl ethers, including methoxy-3,5-bis(trifluoromethyl)benzene and methoxypentafluorobenzene, to give the corresponding aryloxide complexes (PCP)Ir(CH3)(OAr). Although the net reaction is insertion of the Ir center into the C-O bond, density functional theory (DFT) calculations and a significant kinetic isotope effect [kCH3OAr/kCD3OAr = 4.3(3)] strongly argue against a simple insertion mechanism and in favor of a pathway involving C-H addition and ;-migration of the OAr group to give a methylene complex followed by hydride-to-methylene migration to give the observed product. Ethoxy aryl ethers, including ethoxybenzene, also undergo C-O bond cleavage by (PCP)Ir, but the net reaction in this case is 1,2-elimination of ArO-H to give (PCP)Ir(H)(OAr) and ethylene. DFT calculations point to a low-barrier pathway for this reaction that proceeds through C-H addition of the ethoxy methyl group followed by ß-aryl oxide elimination and loss of ethylene. Thus, both of these distinct C-O cleavage reactions proceed via initial addition of a C(sp 3)-H bond, despite the fact that such bonds are typically considered inert and are much stronger than C-O bonds.

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