Synthesis, characterization, and structural determination of polynuclear lithium aggregates and factors affecting their aggregation.

The reaction of [(mu3,mu3-EDBP)Li2]2[(mu3-nBu)Li(0.5Et2O)]2 (1) [EDBP-H2 = 2,2'-ethylidenebis(4,6-di-tert-butylphenol)] with 1 equiv of ROH in toluene gave [(mu3,mu3-EDBP)Li2]2[(mu3-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, [(mu2,mu3-EDBP)2Li4(THF)2][(mu3-nBu)Li] (5). Further reaction of 5 with ROH gave [(mu2,mu3-EDBP)2Li4(THF)3][(mu4-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 [(mu2,mu2-EDBP)Li2(HMPA)2][(mu3-OBn)Li(HMPA)] (9). Compounds [(mu2,mu3-EDBP)2Li4(THF)][(mu4-OCH2CH2OEt)Li]2 (10) and [(mu2,mu2-EDBP)2Li4(mu4-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.