Reorientation Dynamics within Ion-Paired Allylic Lithium Compounds: Isolation of Inversion Processes

Among the several ion−ion reorientational processes that take place within several newly studied allylic lithium compounds, the dynamics of transfer of TMEDA-coordinated lithium between the two allyl faces has been determined independently by use of 13 C NMR line shape studies of diastereotopic geminal methylsilyl groups strategically incorporated close to the chiral lithium in the organometallic species. With increasing temperature, the 13 C shift between these methyls is progressively averaged due to faster rates of lithium transfer (inversion). Typical Δ H ⧧ values of 5−7 kcal·mol - 1 with Δ S ⧧ = ca. −20 eu are encountered. A faster process, the reorientation of coordinated TMEDA on one side of the allyl plane, has been monitored from the NCH 3 13 C resonance of TMEDA-coordinated Li +, with Δ H ⧧ = 7 kcal·mol - 1 and Δ S ⧧ = ca. −12 eu.