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NMR studies of dilithiostyrenes: aggregation, NMR parameters, and DFT calculations for ( E )‐1‐Lithio‐2‐( o ‐lithiophenyl)‐1‐trimethylsilylethene
Author(s) -
Böhler Bernd,
Günther Harald,
Reider Kerstin,
Maercker Adalbert,
Gerbig Dennis,
Hausmann Heike
Publication year - 2017
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.4298
Subject(s) - chemistry , homonuclear molecule , dimer , nmr spectra database , density functional theory , monomer , coupling constant , tetrahydrofuran , carbon 13 nmr , crystallography , computational chemistry , solvent , spectral line , stereochemistry , molecule , organic chemistry , physics , polymer , particle physics , astronomy
The dilithio compound ( E )‐1‐lithio‐2‐( o ‐lithiophenyl)‐1‐trimethylsilylethene ( 5 ) was synthesized from 2‐trimethylsilylbenzo‐[b]tellurophene ( 6 ) with lithium‐6 and a detailed analysis of its 1 H, 6 Li, 13 C, and 29 Si NMR spectra showed 5 to form a dimer 5 2 in tetrahydrofuran and diethylether, while addition of tetramethylethylenediamine stabilizes a monomer 5 1 . A monomer–dimer equilibrium exists with K at 230 K = 1.25 and Δ G 230 o = −0.43 kJ mol −1 . Homonuclear 6 Li, 6 Li coupling of 0.25 ± 0.07 Hz in the dimer was detected by a 1D‐ 6 Li, 6 Li INADEQUATE experiment, and scalar 6 Li, 13 C coupling constants were obtained from 13 C satellites in the 6 Li spectrum, from 13 C multiplet simulation and 6 Li, 13 C‐HMQC spectra. In addition, structures and coupling constants of 5 1 and 5 2 were calculated by density functional theory (DFT) methods. It was found that the magnitude of the 6 Li, 13 C spin–spin interactions shows an inverse correlation with the C‐Li bond lengths. The intra ‐aggregate exchange in the dimer, caused by 180° rotation of one monomer unit within the solvent cage, was studied by 6 Li DNMR and line shape analysis and yielded Δ G 298 ≠ = 60 ± 3 kJ mol −1 ; ΔH ≠ = 84 ± 3 kJ mol −1 ; ΔS ≠ = 80 ± 3 J mol −1 K −1 for this process. Copyright © 2015 John Wiley & Sons, Ltd.