MeLi + LiCl in THF: One Heterodimer and No Tetramers

Abstract

The structure of the aggregates formed when mixing methyllithium and lithium chloride in THF has been studied by multinuclear magnetic resonance at 170 K. The data suggest that only one new entity is observed, that is the dimer [(MeLi)(LiCl)], in equilibrium (K approximately 0.6) with [MeLi](4) and [LiCl](2). NMR diffusion measurements lead to the conclusion that this dimer is trisolvated in THF at 170 K, a solvation scheme in agreement with DFT computations.

Split Personality of Lithium Chloride: Recent Salt Effects in Organometallic Recipes

“…How LiCl catalyzes the deaggregation of LDA remains a mystery, though Collum envisages either a LDA rung breaking away from a mixed (LDA·LiCl) 2 ladder or a [5] Inhibitions of RLi by molar excesses of LiCl are also noted by Collum who stresses that the amount of LiCl is a critical factor in the outcome of organolithium reactions. Compelling solution evidence for LiCl-mediated deaggregation of RLi (R = Me) comes from the combined NMR (including DOSY)/DFT study by Maddaluno et al [6] They contend that mixing tetrameric methyllithium with dimeric lithium chloride in THF solution produces a solitary new species in dinuclear (MeLi·LiCl) in the equilibrium mixture. A suspected tris-THF solvate, this cocomplex contains a monomeric fragment of MeLi.…”

Transition‐Metal‐Free Heterobiaryl Synthesis via Aryne Coupling

“…The previous investigation evaluating the effect of ligands clearly underlined influences of such compounds on the reactivity of organolithiums. [44] In this context, "salt effects" have attracted significant interest in recent years, leading to comprehensive spectroscopic and theoretical investigations, [71][72][73][74][75][76][77][78][79][80][81] more specifically in organolithium chemistry where the effects of lithium halides are commonly encountered. [82][83][84][85][86][87][88][89][90][91][92][93][94][95] Lithium salts are undoubtedly among the most widely studied salts, being ubiquitous in a large number of lithiation reactions -either because they are generated in the reaction, or because they are involuntarily brought by a contaminated commercial source.…”

A Combined 1H/6Li NMR DOSY Strategy Finally Uncovers the Structure of Isopropyllithium in THF

“…The 13 C signal of the major species (at 12.7 ppm) is a 1:2:3:2:1 quintet ( 1 J 13C−6Li =7.5 Hz), typical of a carbon atom surrounded by two equivalent Li cations. Among the most classically encountered oligomers, a cyclic homodimer ([ i PrLi] 2 2 , Figure ) and a cyclic homotrimer ([ i PrLi] 3 3 , Figure ) can fit this multiplicity . The plausible presence of LiCl, the by‐product of the i Pr 6 Li synthesis (page 4S in Supporting Information), led us to also take into account the 1:1 i PrLi/LiCl cyclic mixed‐dimer ([( i PrLi)(LiCl)] 4 , Figure ).…”

“…This strategy required the selection of proper lithiated internal references to be added to our i PrLi sample. Methyllithium, that is known to provide a tetramer in THF and to form [(RLi) m (MeLi) n ] mixed complexes (with m and n ≥0 and 1≤ m + n ≤4), was retained . A 1:1 mixture of i PrLi and MeLi was first characterized (pages 19S to 27S in Supporting Information) through a series of standard NMR experiments at −103 °C.…”