title: Activation of an alkyl C-H bond geminal to an agostic interaction: an unusual mode of base-induced C-H activation.
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 (i)Pr 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 DeltaE (double dagger)(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.
authors.affiliation: School of Engineering and Physical Sciences, Perkin Building, Heriot-Watt University, Edinburgh, EH14 4AS, UK.
authors.forename: L Jonas L
authors.initials: LJ
authors.lastname: Häller
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Page
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Macgregor
authors.forename: Mary F
authors.initials: MF
authors.lastname: Mahon
authors.forename: Michael K
authors.initials: MK
authors.lastname: Whittlesey