Formation of Organolithium Hetero‐Aggregates [Li 4 Ar 2 ( n Bu) 2 ] (Ar=C 6 H 4 CH(Me)NMe 2 ‐2) during the Directed ortho ‐Lithiation of [1‐(Dimethylamino)ethyl]benzene

• Published in: Chemistry : a European journal Vol. 11; no. 1; pp. 253 - 261
• Main Authors: Kronenburg, Claudia M. P., Rijnberg, Evelien, Jastrzebski, Johann T. B. H., Kooijman, Huub, Lutz, Martin, Spek, Anthony L., Gossage, Robert A., van Koten, Gerard
• Format: Journal Article
• Language: English
• Published: 01.01.2005
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200400828

Abstract ( R )‐[1‐(Dimethylamino)ethyl]benzene reacts with n BuLi in a 1:1 molar ratio in pentane to quantitatively yield a unique hetero‐aggregate ( 2 a ) containing the lithiated arene, unreacted n BuLi, and the complexed parent arene in a 1:1:1 ratio. As a model compound, [Li 4 (C 6 H 4 CH(Me)NMe 2 ‐2) 2 ( n Bu) 2 ] ( 2 b ) was prepared from the quantitative redistribution reaction of the parent lithiated arene Li(C 6 H 4 CH(Me)NMe 2 ‐2) with n BuLi in a 1:1 molar ratio. The mono‐Et 2 O adduct [Li 4 (C 6 H 4 CH(Me)NMe 2 ‐2) 2 ( n Bu) 2 (OEt 2 )] ( 2 c ) and the bis‐Et 2 O adduct [Li 4 (C 6 H 4 CH(Me)NMe 2 ‐2) 2 ( n Bu) 2 (OEt 2 ) 2 ] ( 2 d ) were obtained by re‐crystallization of 2 b from pentane/Et 2 O and pure Et 2 O, respectively. The single‐crystal X‐ray structure determinations of 2 b – d show that the overall structural motifs of all three derivatives are closely related. They are all tetranuclear Li aggregates in which the four Li atoms are arranged in an almost regular tetrahedron. These structures can be described as consisting of two linked dimeric units: one Li 2 Ar 2 dimer and a hypothetical Li 2 n Bu 2 dimer. The stereochemical aspects of the chiral Li 2 Ar 2 fragment are discussed. The structures as observed in the solid state are apparently retained in solution as revealed by a combination of cryoscopy and 1 H, 13 C, and 6 Li NMR spectroscopy.