CRYSTAL-STRUCTURE OF ALPHA-(TRIMETHYLSILYL)BENZYLLITHIUM.TETRAMETHYLETHYLENEDIAMINE [C6H5CH(SIME3)LI.TMEDA] AND ALPHA-(PHENYLTHIO)BENZYLLITHIUM.3TETRAHYDROFURAN [C6H5CH(SPH)LI.(THF)3] - 2 BENZYLLITHIUM COMPOUNDS WITH CENTRAL CHIRALITY

The crystal structure analyses of [C6H5CH(SiMe3)Li . TMEDA] (6) and of [C6H5CH(SPh)Li . (THF)3] (7), in which the positions of the benzylic hydrogen atoms have been determined experimentally, reveal compounds with pyramidal benzylic carbon atoms. In 6 lithium is eta-2-bound to C(ipso) and C-alpha of the substituted benzylic anion which leads, together with the TMEDA molecule, to a tetra-coordinated lithium atom. In 7 only one Li-C bond is formed, namely that to C-alpha. Additional coordination with three THF molecules results also in a tetracoordinated lithium atom. The extent of the pyramidalization in 6 and 7 is qualitatively in agreement with quantum-mechanical ab initio calculations [G86, MP2/6-311 + + G(d,p)].