Synthesis, characterization, and catalysis of mixed-ligand lithium aggregates, excellent initiators for the ring-opening polymerization of L-lactide.

Three novel mixed-ligand lithium aggregates, [(mu(3)-EDBP)Li(2)](2)[(mu(3)-(n)Bu)Li(0.5Et(2)O)](2) (1), [(mu(3)-EDBP)Li(2)](2)[(mu(3)-OBn)Li](2) (2), and [(mu(3)-EDBP)Li(2)](2)[(mu(3)-OCH(2)CH(2)OCH(2)CH(3))Li](2) (3), have been synthesized and structurally characterized. The reaction of 2,2'-ethylidene-bis(4,6-di-tert-butylphenol) (EDBP-H(2)) with 3.6 molar equiv of (n)BuLi gives 1 in high yield. 1 further reacts with benzyl alcohol and 2-ethoxyethanol respectively to yield the corresponding products 2 and 3. Experimental results show that 2 and 3 efficiently initiate the ring-opening polymerization of L-lactide in a controlled fashion, yielding polymers with very narrow polydispersity indexes in a wide range of monomer-to-initiator ratios.