The Aggregation Behavior of Butyllithium in Diethyl Ether in the Presence of LiBr,LiClO4, and Phenyllithium: A Deuterium‐Induced Secondary 6Li‐NMR Isotope‐Effect Study

The aggregation of BuLi (LiR) in diethyl ether (Et₂O) in the presence of LiBr was studied by ⁶Li‐ and ¹³C‐NMR spectroscopy. For a 1.0 : 0.8 mixture of both species, the clusters (LiR)₄, Li₄R₃Br, Li₄R₂Br₂, Li₄RBr₃, and/or Li₂RBr in the ratio 7 : 81 : 12 with Li₄RBr₃ and/or Li₂RBr<1 were detected with the isotopic fingerprint method that is based on secondary deuterium (D)‐induced isotope shifts for δ(Li). The raising content of bromide ions causes increased shielding for δ(Li). As in the case of a 1 : 1 MeLi/LiBr mixture in Et₂O, cluster Li₄R₃Br is the most stable one. In the presence of N,N,N′,N′‐tetramethylethylenediamine (TMEDA), only a mixed dimer was found. For LiClO₄, no inclusion of the ClO$rm{{_{4}^{-}}}$ ion could be detected. A mixture BuLi/PhLi 1 : 1 in Et₂O in the presence of TMEDA showed only dimers with the mixed dimer as the most stable cluster. Chemical exchange of Li between the two homodimers was detected by EXSY spectroscopy. This implies an exchange mechanism with a fluxional tetramer as intermediate.