The Donor‐Base‐Free Aggregation of Lithium Diisopropyl Amide in Hydrocarbons Revealed by a DOSY Method

Abstract

Lithium diisopropyl amide (LDA) is a very prominent reagent that plays a key role in organic synthesis, serving as a base par excellence for a broad range of deprotonation reactions. However, the state of aggregation in solution in the absence of donor bases was unclear. In this paper we solved this problem by employing DOSY NMR experiments based on a newly elaborated external calibration curve (ECC) approach with normalized diffusion coefficients.

New External Calibration Curves (ECCs) for the Estimation of Molecular Weights in Various Common NMR Solvents

“…Those ECCs have been used successfully to determine the aggregation state of sodium indenide in THF solution . Furthermore the identification of the oligomeric equilibrium of lithium diisopropylamide (LDA) in toluene solution was achieved with ECCs . To expand the applicability of the method, we now introduce new ECCs for additional widely used NMR solvents: [D 6 ]DMSO, C 6 D 6 , CDCl 3 , CD 2 Cl 2 , and C 6 D 12 .…”

Applications of NMR diffusion methods with emphasis on ion pairing in inorganic chemistry: a mini‐review

“…The most popular applications involving NMR diffusion methods concern themselves with directly estimating a molecular weight (MW) frequently with the help of model compounds, as indicated in Fig. .…”

Introducing a Hydrogen‐Bond Donor into a Weakly Nucleophilic Brønsted Base: Alkali Metal Hexamethyldisilazides (MHMDS, M=Li, Na, K, Rb and Cs) with Ammonia

“…In CsHMDS the direct solvation number of ammonia is decreased giving the disolvated CsHMDS dimer 5 , where open coordination sites are stabilised by several s‐block Si−CH 3 ⋅⋅⋅Cs interactions at the expense of an ammonia coordination. Reactivity and aggregation studies in solution, including external calibration curve (ECC) molecular weight determinations are in progress.…”