NMR studies of dilithiostyrenes: aggregation, NMR parameters, and DFT calculations for ( E )‐1‐Lithio‐2‐( o ‐lithiophenyl)‐1‐trimethylsilylethene

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.