Tridentate Anilido-Aldimine Magnesium and Zinc Complexes as Efficient Catalysts for Ring-Opening Polymerization of epsilon-Caprolactone and L-Lactide

Abstract

A novel tridentate anilido-aldimine ligand, [o-C(6)H(4)(NHAr)-HC= NCH(2)CH(2)NMe(2)] (Ar = 2,6-(i)Pr(2)C(6)H(3), L-H, 1), has been prepared by the condensation of N, N-dimethylethylenediamine with one molar equivalent of 2-fluoro-benzaldehyde in hexane, followed by the addition of the lithium salt of diisopropylaniline in THE Magnesium (Mg) and zinc (Zn) complexes supported by the tridentate anilido-aldimine ligand have been synthesized and structurally characterized. Reaction of L-H (1) with an equivalent amount of Mg(n)Bu(2) or ZnEt(2) produces the monomeric complex [LMg(n)Bu] (2) or [LZnEt] (3), respectively. Experimental results show that complexes 2 and 3 are efficient catalysts for ring-opening polymerization of epsilon-caprolactone (CL) and L-lactide (LA) in the presence of benzyl alcohol and catalyze the polymerization of epsilon-CL and L-LA in a controlled fashion yielding polymers with a narrow polydispersity index. In both polymerizations, the activity of Mg complex 2 is higher than that of Zn complex 3, which is probably due to the higher Lewis acidity and better oxophilic nature of Mg(2+) metal. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47:4927-4936, 2009