Structure of dilithio-(E)-1,4-bis(trimethylsilyl)but-2-ene by X-ray crystallography and 1H-7Li HOESY

Leslie D. Field*, Michael G. Gardiner, Barbara A. Messerle, Colin L. Raston

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)

Abstract

1H-7Li HOESY spectra of good spectral quality were obtained on [{Li(TMEDA)}2{(Me3SiCH=CH)2}] (1) and [{Li(TMEDA)}2{(Me3SiCH=CMe)2}] (2) in solution at room temperature. Fluxionality leads to motional averaging of the environment around the Li nucleus and consequently a reduction in the quadrupolar contribution to 7Li relaxation. Measured 7Li relaxation times in 1 and 2 were temperature dependent, but relatively long T1 values (ca. 500 ms near ambient temperature) permitted the observation of 7Li-1H HOESY spectra. This is the first report of 7Li-1H HOESY NMR for obtaining structural information. X-ray diffraction data for 1 established a planar (Z)-butenediyl unit, with essentially double-bond character across C2 and C3 (1.34 (3) Å) and concentration of charge on the terminal carbons (Si-C1 = 1.76 (1) Å, C1-C2 = 1.47 Å), with the lithium atoms residing symmetrically over the vector between these carbon atoms. Crystals of 1 are orthorhombic, space group Pbca, a - 10.711 (1) Å, b = 15.393 (3) Å, c = 19.941 (3) Å, V = 3287.8 (9) Å3, Z = 4. Cross-peak volumes for the Li-butenediyl fragment of 1 measured in 7Li-1H HOESY spectra in solution are consistent with the X-ray data. The combination of NMR spectroscopy and X-ray structural analysis established a double-bridging lithium structure with similar geometries for both 1 and 2.

Original languageEnglish
Pages (from-to)3566-3570
Number of pages5
JournalOrganometallics
Volume11
Issue number11
Publication statusPublished - 1992
Externally publishedYes

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