Anionic polymerization of acrylic monomers. 18. NMR characterization of a unique complex between lithium 2-(2-methoxyethoxy) ethoxide and methyl α-lithioisobutyrate

A unique ligand-promoted-loose mixed complex MIB-(Li-3(OEEM)(2))(+) has been characterized for the first time by means of NMR spectroscopy in solution. This new complex, which is a dual mu/sigma one, is obviously different from either a simple tight mu-mixed complex, such as nMIBLi.mX (X = Cl or OtBu), or a sigma-cation-binding one with mole charge separation, such as K211/MIBLi. It originates from a simultaneous dual complexation (mu/sigma) of MIBLi by both the lithium alkoxide (mu-mixed complexation) and the chelating polyether components (sigma-cation-binding complexation) of LiOEEM. Furthermore, it has been demonstrated; that, whichever the solvent, i.e., toluene, a 9/1 toluene/THF mixture, or THF, complexation of MIBLi by greater than or equal to 2 mol equiv of LiOEEM produces the same type of complex, i.e., MIB-(Li-3(OEEM)(2))(+), suggesting that, in this strong complex, the lithium cations are strongly coordinated by the ligand.