STRUCTURE OF ALPHA-(DIMETHYLAMINO)BENZYLLITHIUM IN SOLUTION - DYNAMIC EQUILIBRIUM BETWEEN AN ETA-1 AND AN ETA-3 SPECIES

Temperature-dependent H-1- and C-13-NMR-spektroscopic shifts observed in tetrahydrofuran are indicative of an equilibrium between a high-temperature eta-3 and a low-temperature eta-1 species. MNDO calculations are in accord with this view, and HOESY experiments proof it, too. The equilibrium is controled by solvation or complexation, low Lewis basicity of the solvent or bidentate ligands favoring the eta-3, high Lewis basicity or tridentate ligands the eta-1 species. Equilibrium as well as rate constants have been estimated, and from their temperature dependence the thermodynamics of the equilibrium and the activation barriers were calculated.