NMR spectroscopy of organolithium compounds, part XXXIII : trans ‐2,3‐dimethylcyclopropyllithium aggregation in diethylether: An equilibrium between three different complexes of comparable energy and the influence of LiBr on aggregate structure

The aggregate formation of trans ‐2,3‐dimethylcyclopropyllithium ( 2 ) was studied in diethylether (DEE). With the help of the isotopic fingerprint method three clusters, a monomer , a dimer , and a fluxional tetramer in the ratio 1.00:0.53:0.22 were identified at 187 K. In the presence of 1 equivalent of LiBr cyclopropyllithium ( 1 ) forms in DEE at 163 K a mixed dimer and a mixed tetramer, while in THF a mixed dimer dominates. Under the same conditions 2 and 2,2,3,3‐tetramethylcyclopropyllithium ( 3 ) form in the solvent mixture DEE/THF (1:1) mixed dimers, as does 2 also in THF.