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

Abstract

Despite its common use in synthesis, the structure of isopropylliyhium in THF has never been determined, a dimer being generally proposed but not supported. This paper fills this data gap through a sophisticated NMR study that shows that, in THF at low-temperature, isopropyllithium is in the form of a 1:2 mixture of a trisolvated monomer and a disolvated dimer in equilibrium. The presence of the monomer, never evoked before, together with a hypo-solvation of the dimer hinted by DFT calculations, provides a rational explanation to the remarkable reactivity of this organolithium reagent in ethereal solvents.

Synthesis and Identification of Aryl and Alkyl Gem‐Dilithium Phosphido‐Boranes: A Boost to the Chemistry of Phosphandiides

“…Therefore, the penta-solvated monomer Li 2 [PhP·BH 3 ]·5 THF should be the most likely speciesi nT HF. Note that an accurate measurement of the solvation values by DOSY techniques is, as for other organolithium species, [11] limited by the dynamic of Li-THF interactions.…”

NMR spectroscopy of organolithium compounds, part XXXIII: trans‐2,3‐dimethylcyclopropyllithium aggregation in diethylether: An equilibrium between three different complexes of comparable energy and the influence of LiBr on aggregate structure

“…1 J ( 13 C, 6 Li) data around 17 Hz are abundant for halogen‐lithium carbenoids, but the formation of higher aggregates is here prevented by the substituent X in the C‐1(Li,X) fragment. Recently published examples of monomer stabilization by THF were found for trisolvated 1‐penylcyclopropyllithium and trisolvated iso ‐propyllithium . In DEE/THF (1:1), the methyl‐substituted cyclopropyl compounds 2 and 3 form only dimers …”

Triangles and Squares for a Unique Molecular Crystal Structure: Unsupported Two‐Coordinate Lithium Cations and CC Agostic Interactions in Cyclopropyllithium Derivatives

“…The nature of 1 is unchanged in a non‐coordinating, non‐polar solvent solution. Although we have not used the most advanced and accurate ECC‐DOSY NMR methods, 1 H DOSY NMR spectroscopy in [D 6 ]benzene at room temperature coupled with a diffusion coefficient‐formula weight ( D ‐FW) correlation analysis yielded an estimated FW of 470±47 g mol −1 (Figure ). This result fits nicely with the calculated FW of the tetramer of 1 which is 480.8 g mol −1 , emphasizing the stability of the aggregate.…”