Formation of Organolithium Hetero-AggregatesLi4Ar2(wBu)_2(Ar = C6H4CH(Me)NMe2-2)during the Directed orf/io-Lithiation of1-(Dimethylamino)ethylbenzene

摘要

(R)-1-(Dimethylamino)-ethyljbenzene reacts with "BuLi in a 1:1 molar ratio in pentane to quantitatively yield a unique hetero-aggregate(2 a)containing the lithiated arene,un-reacted "BuLi,and the complexed parent arene in a 1:1:1 ratio.As a model compound,Li4(C6H4CH-(Me)NMer2)_2(nBu)J(2b)was prepared from the quantitative redistribution reaction of the parent lithiated arene Li(C6H4CH(Me)NMer2)with "BuLi in a 1:1 molar ratio.The mono-Et2O adductLi4(C6H4CH(Me)NMer2)_2("Bu)_2(OEt2)(2c)and the bis-Et2O adductLi4(C6H4CH(Me)NMe2-2)_2-("Bu)_2(OEt2)_2(2d)were obtained by re-crystallization of 2b from pentane/ Et2O and pure Et2O,respectively.The single-crystal X-ray structure determinations of 2b-d show that the overall structural motifs of all three derivatives are closely related.They are all tetra-nuclear 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 Li2"Bu2 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 cryosco-py and 'H,13C,and 6Li NMR spectros-copy.