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 C-13 NMR line shape studies of diastereotopic geminal methylsilyl groups strategically incorporated close to the chiral lithium in the organometallic species. With increasing temperature, the C-13 Shift between these methyls is progressively averaged due to faster rates of lithium transfer (inversion). Typical Delta H-double dagger values of 5-7 kcal.mol(-1) with Delta S-double dagger = 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 NCH3 C-13 resonance of TMEDA-coordinated Li+, with Delta H-double dagger = 7 kcal.mol(-1) and Delta S-double dagger = ca. -12 eu.