PARTIALLY DELOCALIZED ALLYLIC LITHIUM COMPOUNDS - DYNAMICS OF INVERSION, 1,3-LI SHIFT, AND C-LI BOND, EXCHANGE INFLUENCE OF THE STEREOCHEMISTRY OF SOLVATION

While exo-exo-[1,3-bis(trimethylsilyl)allyl]lithium (15) and [1-(trime thylsilyl)allyl]lithium (16) were previously shown to be contact ion p airs containing delocalized carbanions, the corresponding species with a pendant ligand at the 2-position, [2-[[bis(2-methoxyethyl)amino]met hyl]-1, (14) and ethyl)amino]methyl]-1-(trimethylsilyl)ally]lithium (1 2), respectively, appear from their C-13 NMR shifts and the first obse rvation of C-13 lithium spin coupling in an allylic lithium to be part ially delocalized with detectable C-Li covalence. In proposed structur es 12 and 14, lithium is tridentately complexed. N and Li lie within t he allyl carbon plane with the two oxygens normal to it on opposite si des. NMR line shape analysis and C-13(1) Of Signal averaging of the C- 13-Li-6 coupling of 12 provides dynamics of intermolecular C-Li bond e xchange with Delta H-e(double dagger) and Delta S-double dagger of 11. 6 kcal/mol and -11.5 eu, respectively. Inversion at the lithium-bound carbon of 12 averages nonequivalent ligand shifts. Line shape analysis gives Delta H-i(double dagger) and Delta S-i(double dagger) of 8 kcal /mol and -10 eu, respectively. Line shape changes observed for the met hylsilyl (C-13 and H-1) resonances as well as of the terminal C-13's O f 14 due to a 1,3 Li sigmatropic shift yield activation parameters Del ta H-s(double dagger) and Delta S-s(double dagger) of 18 kcal/mol and +15 eu. These results show that electronic structure of nominally conj ugated organolithium compounds can be significantly altered by changin g the stereochemistry of solvation, by use of pendant ligands, produci ng structures previously described in other systems as transition stat es for allylic rotation.