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.
Haller, L. J. L., Page, M. J., Macgregor, S. A., Mahon, M. F., & Whittlesey, M. K. (2009). Activation of an alkyl C-H bond geminal to an agostic interaction: an unusual mode of base-induced C-H activation. Journal of the American Chemical Society, 131(13), 4604-4605. https://doi.org/10.1021/ja900953d