Formation of Organolithium Hetero‐Aggregates [Li4Ar2(nBu)2] (Ar=C6H4CH(Me)NMe2‐2) during the Directed ortho‐Lithiation of [1‐(Dimethylamino)ethyl]benzene

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Abstract
(R)‐[1‐(Dimethylamino)ethyl]benzene reacts with nBuLi in a 1:1 molar ratio in pentane to quantitatively yield a unique hetero‐aggregate (2 a) containing the lithiated arene, unreacted nBuLi, and the complexed parent arene in a 1:1:1 ratio. As a model compound, [Li4(C6H4CH(Me)NMe2‐2)2(nBu)2] (2 b) was prepared from the quantitative redistribution reaction of the parent lithiated arene Li(C6H4CH(Me)NMe2‐2) with nBuLi in a 1:1 molar ratio. The mono‐Et2O adduct [Li4(C6H4CH(Me)NMe2‐2)2(nBu)2(OEt2)] (2 c) and the bis‐Et2O adduct [Li4(C6H4CH(Me)NMe2‐2)2(nBu)2(OEt2)2] (2 d) were obtained by re‐crystallization of 2 b from pentane/Et2O and pure Et2O, 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 Li2Ar2 dimer and a hypothetical Li2nBu2 dimer. The stereochemical aspects of the chiral Li2Ar2 fragment are discussed. The structures as observed in the solid state are apparently retained in solution as revealed by a combination of cryoscopy and 1H, 13C, and 6Li NMR spectroscopy.

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