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