Synthesis of amine-bridged bis(phenolate) rare-earth metal alkoxides and their catalytic performance for the polymerization of trimethylene carbonate and L‑lactide

Abstract

A series of rare-earth metal complexes stabilized by amine-bridged bis(phenolate) ligand were synthesized and employed as initiators for the polymerization of trimethylene carbonate (TMC) and L‑lactide (L-LA). One-pot reaction of the amine-bridged bis(phenol) LH2 (L = (CH3)2NCH2CH2N[CH2-(2-OH-3-tBu-5-OMe-C6H2)]2) with (C5H5)3RE(THF) or Nd[N(SiMe3)2]3 in a 1:1 molar ratio, followed by the treatment of 1 equiv. of ROH (R = (CF3)2CH, CF3CH2) gave the amine bridged bis(phenolate) rare-earth metal alkoxides LRE(OCH(CF3)2)(THF)n (RE = La (1), n = 2; RE = Nd (2), Y (3), Yb (4), Lu (5), n = 1) and LNd(OCH2CF3)(THF)2 (6) in good isolated yields. These complexes were efficient initiators for the homopolymerization of both TMC and L-LA. Kinetics of the polymerization of TMC and L-LA initiated by complex 6 was investigated, and the results showed that the polymerizations of L-LA and TMC were first order for the initiator and monomer concentrations.