Solution-Structure and Aggregation Behavior of Two Dilithiostyrene Derivatives

The solution structure and the aggregation behavior of (E)‐2‐lithio‐1‐(2‐lithiophenyl)‐1‐phenylpent‐1‐ene (1) and (Z)‐2‐lithio‐1‐(2‐lithiophenyl)ethene (2) were investigated by one‐ and two‐dimensional 1H‐, 13C‐, and 6Li‐NMR spectroscopy. In Et2O, both systems form dimers which show homonuclear scalar 6Li,6Li spin‐spin coupling. In the case of 2, extensive 6Li,1H coupling is observed. In tetrahdrofuran and in the presence of 2 mol of N,N,N′,N′‐tetramethylethylylenediamine (tmeda), the dimeric structure of 1 coexists with a monomer. The activation parameters for intra‐aggregate exchange in the dimers of 1 and 2 (1 (Et2O): ΔH≠ = 62.6 ± 13.9 kJ/mol, ΔS≠ = 5.8 ± 14.0 J/mol K, ΔG≠(263) = 61.1 kJ/mol; 2 (dimethoxyethane): ΔH≠ = 36.9 ± 6.5 kJ/mol, ΔS≠ = −61 ± 25 J/mol K, ΔG≠(263) = 54.0 kJ/mol) and the thermodynamic parameters for the dimer‐monomer equilibrium for 1 (ΔH°; = 26.7 ± 5.5 kJ/mol, ΔS° = 63 ± 27 J/mol K), where the monomer is favored at low temperature, were determined by dynamic NMR studies.