Ligand Binding Constants to Lithium Hexamethyldisilazide Determined by Diffusion-Ordered NMR Spectroscopy

We
report the direct measurement of ligand-binding constants of
organolithium complexes using a 1H NMR/diffusion-ordered
NMR spectroscopy (DOSY) titration technique. Lithium hexamethyldisilazide
complexes with ethereal and ester donor ligands (THF, diethyl ether,
MTBE, THP, tert-butyl acetate) are characterized
using 1H NMR and X-ray crystallography. Their aggregation
and solvation states are confirmed using diffusion coefficient–formula
weight correlation analysis, and the 1H NMR/DOSY titration
technique is applied to obtain their binding constants. Our work suggests
that steric hindrance of ethereal ligands plays an important role
in the aggregation, solvation, and reactivity of these complexes.
It is noteworthy that diffusion methodology is utilized to obtain
binding constants.