Rare earth metal bisamido complexes with an NNO tridentate ligand and catalytic activity for the selective polymerization of isoprene

Abstract

The reaction of 4-((2-(pyridin-2-yl)ethyl)imino)pent-2-en-2-ol (HL, 1) with 1 equiv. of [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)₃ produces rare earth metal bisamido complexes incorporating the pyridyl-functionalized β-ketoiminato NNO tridentate ligand [LRE{[N(SiMe₃)₂]₂}] (L = CH₃C(O)CHC(CH₃)NCH₂CH₂(2-C₅H₄N), RE = Y (2), Nd (3), Sm (4), Gd (5), Dy (6), Er (7) and Yb (8)). All the complexes were fully characterized via elemental and spectroscopic analyses, and their structures were further determined via single-crystal X-ray diffraction study. Additionally, complexes 2–8 were investigated as precatalysts for isoprene polymerization. The results showed that except for complexes 4 and 8, all the complexes could effectively initiate the polymerization of isoprene to afford polyisoprene with high regio- and stereo-selectivity (1,4-cis selectivity up to 97.1%) in the presence of cocatalysts.