Vigilancia Tecnológica

Six rare earth alkoxides bearing amine?bridged bis(phenolato) ligands were synthesized in this work, all of which showed good activity in the ROP of rac?BBL. Among them, complex 3 bearing bulky o?1,1?diphenylethyl substituents was highly efficient (TOF up to 27,300?h?1) and led to highly syndiotactic PHB (Pr up to 0.86).A series of rare earth alkoxides bearing amine?bridged bis(phenolato) ligands were synthesized through sequential reactions of RE(C5H5)3(THF) (RE = Y, Lu) or Nd[N(SiMe3)2]3 with bis(phenols) LH2 and CF3CH2OH. Complexes REL(OCH2CF3)(THF)n (1–6) bearing different aryl?substituents were obtained in good yields of 59–70?%. They were applied in the ring?opening polymerization (ROP) of rac???butyrolactone (rac?BBL), which showed good activity (TOF up to 27,300?h?1), resulting in syndiotactically enriched poly(3?hydroxybutyrate) (PHB) (Pr up to 0.86) with narrow polydispersities (PDI ? 1.27). The yttrium complex 3 bearing bulky o?1,1?diphenylethyl substituents outperformed other complexes, suggesting that the smaller ionic radii of metal centers and bulky ortho substituents of ancillary ligands play crucial roles in controlling the activity and stereoselectivity in ROP of rac?BBL. Kinetics of the polymerization of rac?BBL initiated by complex 3 was investigated, which revealed first order dependences on the monomer and initiator concentrations, respectively.