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

Abstract

The reaction of [(mu(3), mu(3)-EDBP)Li-2](2)[(mu(3)-Bu-n)Li(0.5Et(2)O)](2) (1) [EDBP-H-2 = 2,2'-ethylidenebis(4,6-di-tert-butylphenol)] with 1 equiv of ROH in toluene gave [(mu(3),mu(3)-EDBP)Li-2](2)[(mu(3)-OR)Li](2) [R = Bn (2), CH2CH2OEt (3), and Bu-n (4)]. In the presence of 3 equiv of tetrahydrofuran (THF), the hexanuclear compound 1 slowly decomposed to an unusual pentanuclear Li complex, [(mu(2),mu(3)-EDBP)(2)Li-4(THF)(2)][(mu(3)-Bu-n)Li] (5). Further reaction of 5 with ROH gave [(mu(2),mu(3)-EDBP) Li-2(4)(THF)(3)][(mu(4)-OR)Li] [R = Bn (6), Bu-n (7), and CH2CH2OEt (8)] without a major change in its skeleton. Treatment of 2 with an excess of hexamethylphosphoramide (HMPA) yields [(mu(2),mu(2)-EDBP)Li-2(HMPA)(2)][(mu(3)-OBn)-Li(HMPA)] (9). Compounds [(mu(2),mu(3)-EDBP)(2)Li-4(THF)][(mu(4)-OCH2CH2OEt)Li](2) (10) and [(mu(2),mu(2)-EDBP)(2)Li-4(mu(4)-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.