Lanthanum complexes stabilized by a pentadentate Schiff-base ligand: synthesis, characterization, and reactivity in statistical copolymerization of epsilon-caprolactone and L-lactide

摘要

Developing catalysts that are capable of catalyzing the copolymerization of epsilon-caprolactone and t-lactide to give random CL/LA copolymers is of great importance. One-pot reaction of La[N(SiMe3)(2)](3) with 1 equiv. of LH2 (LH2 = NH(CH2CH2N=CHC6H2-3,5(t)Bu(2)-2-OH)(2)) in THE at room temperature, followed by protolysis with one equivalent amount of ROH (R = C6H2-2,6(t)Bu(2)-4-CH3, Bu-t, Pr-i, Bn, and Et) at 60 degrees C gave the mono-Schiff-base-ligated lanthanum aryloxide complex LLa(OC6H2-2,6-Bu-t(2)-4-CH3)(THF) (1), and lanthanum alkyloxide complexes (LLaOBu)-Bu-t(THF) (2), (ILLaOPr)-Pr-i](2) (3), (LLaOBn](2) (4), and (LLaOEt](2) (5) in 59-69% isolated yields. These lanthanum complexes were capable of initiating the homopolymerization of L-lactide and rac-lactide with extremely high activity, and the copolymerization of epsilon-caprolactone (epsilon-CL) and L-lactide (L-LA) to give statistical CL/LA copolymers via a transesterification reaction.