TY - JOUR
T1 - Structure of dilithio-(E)-1,4-bis(trimethylsilyl)but-2-ene by X-ray crystallography and 1H-7Li HOESY
AU - Field, Leslie D.
AU - Gardiner, Michael G.
AU - Messerle, Barbara A.
AU - Raston, Colin L.
PY - 1992
Y1 - 1992
N2 -
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.
AB -
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.
UR - http://www.scopus.com/inward/record.url?scp=0011454096&partnerID=8YFLogxK
M3 - Article
AN - SCOPUS:0011454096
SN - 0276-7333
VL - 11
SP - 3566
EP - 3570
JO - Organometallics
JF - Organometallics
IS - 11
ER -