Diastereoselective Self-Assembly of Chiral Diamine-Chelated Aryllithiums to Dimeric Aggregates

Abstract

, and [LiC6H4(CH(Me)N(Me)CH2CH2NMe2-(rac))-2]2 ((rac)-3b) were synthesized and characterized in the solid state and in solution. X-ray crystallographic studies of 2b and (R)-3b and molecular weight determinations of 2b, (R)-3b, and (rac)-3b by cryoscopy in benzene showed that, both in the solid state and in apolar, noncoordinating solvents such as benzene, these compounds exist as discrete dimeric aggregates. For (R)-3b and (rac)-3b the aggregation process of two monomeric aryllithium units to one dimer is highly diastereoselective.

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

“…Rac-17 gives, upon lithiation, a different kind of self-assembly in which only Li centres of opposing chirality (at C) self-assemble to form the dimer. Further discussions of this unusual aggregation behaviour have been disclosed [89,90].…”

“…, chirality in this case again being defined only at lithium [89]. Thus, steric effects can induce and control these self-assembled (chiral) organolithium pincer dimers.…”

“…(R)-17: the chiral carbon is marked with an asterisk for clarity) or its racemic (R/S) counterpart rac-17 (chirality here being defined at the benzylic C-position). Upon lithiation of the enantiopure aryl-bromide (R)-17, the dimer which is formed is again exclusively meso at Li (like 16), and hence this secondary chiral centre has no effect on the induced chirality at the Li centres [89]. Rac-17 gives, upon lithiation, a different kind of self-assembly in which only Li centres of opposing chirality (at C) self-assemble to form the dimer.…”

Highlights of 45 years of research: A personal account

“…the benzylic-C center. NMR studies showed that it is this single chiral center that makes the aggregation process of the two monomeric aryllithium units to one dimer highly diastereoselective [31].…”

2 Alkali and alkaline-earth metals

“…Calculations suggested the stable intermediates to be s or p complexes with Li 2 clusters. 22 23 Stereochemical evidence for the mechanism of inversion of amide-substituted benzyllithium compounds (laterally lithiated amides) involving dissociation into a benzyl anion and lithium cation followed by rotation of the amide group to deliver the cation to the other face of the anion with concomitant inversion at the ArCO axis has been presented. 24 The competitive deprotonation (ortho/lateral) of 2-ethyl-N,N-diisopropyl-1-benzamide has been investigated in the context of a link between the number of donor atoms per solvent molecule and reaction chemoselectivity.…”