Lithium indolide (lithioindoline) in THF is shown, by vapor pressure barometry, to be a dimer, and its temperature-dependent, concentration-independent13C chemical shifts are interpreted in terms of the equilibrium Li2A2(THF)2⇆ Li2A2(THF)4(A = amide anion). Lithium 1,2,3,4-tetrahydroquinolide exhibits the same behavior. Lithium 2-methylindolide, 2-methyl-1,2,3,4-tetrahydroquinolide, and A-methyl-, N-n-butyl-, and N-isopropylanilides form the monomer LiA(THF)3as well as the two dimers. Monomer-dimer exchange is slow on the13C NMR time scale at low (<-80 °C) temperatures. Lithium N-(2-methoxyethyl)anilide forms only Li2A2(THF)2. Lithium N-tert-butylanilide exists as LiA(THF)2and LiA(THF)3depending on temperature. All the above salts form only Li2A2(Et20)2in diethyl ether. Both the indolide and N-tert-butylanilide salts exhibit slow E-Z isomerism on the13C NMR time scale at -110 °C.6Li,15N spin-spin couplings of 3.8 and 7.5 Hz are observed for Li2(PhNCH3)2(Et20)2and Li(PhNPr1)(THF)3, respectively, in the corresponding solutions below -80 °C. Rotation of the phenyl group in N-methyl-,N-n-butyl-, N-(2-methoxyethyl)-, and N-isopropyl- but not N-tert-butylanilides is slow on the13C NMR time scale below -50 °C. Rotation of the tert-butyl group in LiA(THF)3(A = N-tert-butylanilide) is comparable with the13C NMR time scale at -100 °C.
ASJC Scopus subject areas
- Colloid and Surface Chemistry