NMR and Quantum-Chemical Study on the Structure of Ester Enolate−Aluminum Alkyl Complexes as Models of the Active Center in the Anionic Polymerization of Methacrylates in Toluene

6 Li and 13 C NMR on ethyl α-lithioisobutyrate (EiBLi) and quantum-chemical (DFT) calculations on methyl α-lithioisobutyrate (MiBLi) were used to elucidate the structure of the active center in the anionic polymerization of methacrylates in the presence of triethylaluminum (AlEt 3 ) in toluene. This study reveals ester enolate/aluminum alkyl complexes with different degrees of association, (MiBLi·AlEt 3 ) n ( n = 1, 2, 4), and different stoichiometries, MiBLi· x AlEt 3 ( x = 1, 2). In the presence of methyl pivalate (MPiv), which is taken as a model compound for the monomer and polymer, complexes such as (MiBLi·MPiv·AlEt 3 ) n ( n = 1, 2) are formed. These complexes can dissociate into MiBLi·2AlEt 3 and MPiv·AlEt 3 when AlEt 3 is used in excess.