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