Activation of an alkyl C-H bond geminal to an agostic interaction: an unusual mode of base-induced C-H activation

L J L Haller, Michael J Page, S A Macgregor, Mary F Mahon, Michael K Whittlesey

Research output: Contribution to journalArticle

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Abstract

Deuterium labeling studies indicate that base-induced intramolecular C−H activation in the agostic complex 2-D proceeds with exclusive removal of a proton from the methyl arm of an iPr substituent on the N-heterocyclic carbene (NHC) ligand. Computational studies show that this alkyl C−H bond activation reaction involves deprotonation of one of the C−H bonds that is geminal to the agostic interaction, rather than the agostic C−H bond itself. The reaction is readily accessible at room temperature, and a computed activation barrier of ΔE ‡calcd = +11.8 kcal/mol is found when the NHC 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene is employed as the external base. Charge analysis reveals that the geminal hydrogens are in fact more acidic than the agostic proton, consistent with their more facile deprotonation.
LanguageEnglish
Pages4604-4605
Number of pages2
JournalJournal of the American Chemical Society
Volume131
Issue number13
Early online date12 Mar 2009
DOIs
StatusPublished - 8 Apr 2009

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Protons
Deprotonation
Chemical activation
Hydrogen
Deuterium
Ligands
Labeling
Temperature
carbene

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Activation of an alkyl C-H bond geminal to an agostic interaction: an unusual mode of base-induced C-H activation. / Haller, L J L; Page, Michael J; Macgregor, S A; Mahon, Mary F; Whittlesey, Michael K.

In: Journal of the American Chemical Society, Vol. 131, No. 13, 08.04.2009, p. 4604-4605.

Research output: Contribution to journalArticle

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AU - Whittlesey,Michael K

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AB - Deuterium labeling studies indicate that base-induced intramolecular C−H activation in the agostic complex 2-D proceeds with exclusive removal of a proton from the methyl arm of an iPr substituent on the N-heterocyclic carbene (NHC) ligand. Computational studies show that this alkyl C−H bond activation reaction involves deprotonation of one of the C−H bonds that is geminal to the agostic interaction, rather than the agostic C−H bond itself. The reaction is readily accessible at room temperature, and a computed activation barrier of ΔE ‡calcd = +11.8 kcal/mol is found when the NHC 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene is employed as the external base. Charge analysis reveals that the geminal hydrogens are in fact more acidic than the agostic proton, consistent with their more facile deprotonation.

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