Synthesis, Characterization, and Structural Determination of Polynuclear Lithium Aggregates and Factors Affecting Their Aggregation

The reaction of [(μ3,μ3-EDBP)Li2]2[(μ3-nBu)Li(0.5Et2O)]2 (1) [EDBP-H2 = 2,2‘-ethylidenebis(4,6-di-tert-butylphenol)]
with 1 equiv of ROH in toluene gave [(μ3,μ3-EDBP)Li2]2[(μ3-OR)Li]2 [R = Bn (2), CH2CH2OEt (3), and nBu (4)]. In
the presence of 3 equiv of tetrahydrofuran (THF), the hexanuclear compound 1 slowly decomposed to an unusual
pentanuclear Li complex, [(μ2,μ3-EDBP)2Li4(THF)2][(μ3-nBu)Li] (5). Further reaction of 5 with ROH gave [(μ2,μ3-EDBP)2Li4(THF)3][(μ4-OR)Li] [R = Bn (6), nBu (7), and CH2CH2OEt (8)] without a major change in its skeleton.
Treatment of 2 with an excess of hexamethylphosphoramide (HMPA) yields [(μ2,μ2-EDBP)Li2(HMPA)2][(μ3-OBn)Li(HMPA)] (9). Compounds [(μ2,μ3-EDBP)2Li4(THF)][(μ4-OCH2CH2OEt)Li]2 (10) and [(μ2,μ2-EDBP)2Li4(μ4-OCH2CH2OEt)(HMPA)]-[Li(HMPA)4]+ (11) can be obtained by the reaction of 3 with an “oxygen-donor solvent” such as
THF and HMPA, respectively. Among the compounds described above, 8 has shown great reactivity toward ring-opening polymerization of l-lactide, yielding polymers with very low polydispersity indexes in a wide range of
monomer-to-initiator ratios.