Lithium complexes supported by amine bis-phenolate ligands as efficient catalysts for ring-opening polymerization of L-lactide

Abstract

Lithium complexes bearing dianionic amine bis( phenolate) ligands are described. Reactions of ligand precursors H2O2NNMe, H2O2NNPy or H2O2NOMe [H2O2NNMe = Me2NCH2CH2N-(CH2-2-HO-3, 5-C6H2(Bu-t)(2))(2); H2O2NNPy = (2-C5H4N)CH2N-(CH2-2-HO-3,5-C6H2(Bu-t)(2))(2); H2O2NOMe = MeOCH2CH2N-(CH2-2-HO-3,5-C6H2(Bu-t)(2))(2)] with 2.2 molar equivalents of (BuLi)-Bu-n in diethylether afford (Li2O2NNMe) 2 (1), (Li2O2NNPy)(2)(2) and (Li2O2NOMe)(2) (3) as tetra-nuclear lithium complexes. The crystalline solids of partially hydrolyzed product, (LiO(HO)NNPy) (4), were obtained from recrystallization of 2 in diethylether solution for three months. The synthesis of (LiO(HO)NOMe)(2) (5) was carried out at ambient temperature by carefully layering a solution of water in hexane on top of a solution of 3 in Et2O. Crystalline solids of 5 were obtained after two months. Molecular structures are reported for compounds 1, 3, 4 and 5. Compounds 1-3 show excellent catalytic activities toward the ring-opening polymerization of L-lactide in the presence of benzyl alcohol.