Stereochemical Aspects of Enantiopure and Racemic Organolithium Aggregates Li₄Ar₄ {Ar = C₆H₄[CH(Me)NMe₂]‐2}

Abstract

Abstract The compounds ( R )‐ and rac ‐[1‐(dimethylamino)ethyl]benzene, ( R )‐ 1 and rac ‐ 1 , respectively, react quantitatively with t BuLi in a 1:1 molar ratio in pentane to give the corresponding ( R )‐ and rac ‐[Li 4 {C 6 H 4 [CH(Me)NMe 2 ]‐2} 4 ], ( R )‐ 2 and rac ‐ 2 , respectively. The same reaction with n BuLi afforded a 1:1:1 aggregate of n BuLi, 2 , and 1 according to the results of quench experiments with H 2 O and D 2 O. The 1 H, 13 C, and 7 Li NMR spectra, as well as the single‐crystal X‐ray structure, reveal that ( R )‐ 2 has a unique self‐assembled tetranuclear structure of two diastereoisomeric dimeric units both in solution, in non‐coordinating hydrocarbon solvents, and in the solid state. Detailed information about rac ‐ 2 , which, in contrast to the high solubility of ( R )‐ 2 , is essentially insoluble in hydrocarbon solvents, was provided by 13 C CP/MAS NMR spectra. We conclude that rac ‐ 2 is a self‐assembled tetranuclear aggregate comprising a combination of two dimeric units, but in this case they are derived from the ( R )‐ and ( S )‐enantiomers, respectively. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)