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

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.

Dramatic enhancement of the stability of rare-earth metal complexes with α-methyl substituted N,N-dimethylbenzylamine ligands

“…Therefore, the metallation was investigated with (S)-phenylethylamine instead of the racemate. The synthesis of the aryllithium reagent was performed using tert-BuLi as deprotonating agent in pentane at room temperature [14].…”

Pincer Complexes of Lithium, Sodium, Magnesium and Related Metals: A Discussion of Solution and Solid-State Aggregated Structure and Reactivity

“…The first structurally elucidated "mixed" pure organolithium aggregate, [(n-BuLi) 2 (2,4,6-tert-Bu 3 C 6 H 2 Li) 2 ], was reported by Power's group in 1993 [161], although it was already well-established that such materials existed in solution [162,163] and were also surmised to be involved in the chemistry of DMBA derivatives [164,165]. The metalation of the carbon atom of the methyl group on position-2 of 2,4,6-trimethyl-1,3-[(dimethylamino)methyl]benzene (40) and the analogous methylene carbon at aromatic position-1 of 1-(2-trimethylsilylethyl)-3,5-dimethyl-2,6-[(dimethylamino)methyl]benzene (41) by a variety of RLi reagents (R ¼ n-Bu, Ph, p-tolyl, tert-Bu) all lead to the formation of 2:2 mixed aggregates [90,166,167].…”

Hetero‐Aggregate Compounds of Aryl and Alkyl Lithium Reagents: A Structurally Intriguing Aspect of Organolithium Chemistry

“…The overall stability of aggregates such as 8 is highlighted by the fact that pure homo-aggregate 7 reacts cleanly in apolar solvents (yield > 90 %) with nBuLi to form a hetero-aggregate (free of 6) that we have been able to isolate in pure form [(dmaebLi) 2 (nBuLi) 2 ] (9) and thereafter fully characterize by solution NMR spectroscopy, cryoscopy, and single-crystal X-ray diffraction (Figure 3). [20] As yield optimization is a vital aspect of synthesis involving in situ formed RLi reagents, the two above examples should serve as a caveat to those using RLi. This situation is especially true in cases where yields are "suspiciously" measured as being 50 % or 75 %; such values suggest the formation of "whole number" hetero-aggregates.…”