Homolysis of the Ln–N (Ln = Yb, Eu) bond. Synthesis, structural characterization and catalytic activity of ytterbium(ii) and europium(ii) complexes with methoxyethyl functionalized indenyl ligands

Abstract

The interaction of methoxyethyl functionalized indene compounds (C₉H₆-1-R-3-CH₂CH₂OMe, R = t-BuNHSiMe₂ (1), Me₃Si (2), H (3)) with [(Me₃Si)₂N]₃Ln(μ-Cl)Li(THF)₃ (Ln = Yb (4), Eu (5)) produced a series of new ytterbium(II) and europium(II) complexes via tandem silylamine elimination/homolysis of the Ln–N (Ln = Yb, Eu) bond. Treatment of the lanthanide(III) amides [(Me₃Si)₂N]₃Ln(μ-Cl)Li(THF)₃ (Ln = Yb (4), Eu (5) with 2 equiv. of 1, 2 and 3, respectively, produced, after workup, the ytterbium(II) complexes [η⁵:η¹-Me₂Si(MeOCH₂CH₂C₉H₅)(NHBu-t)]₂Yb^II (6), (η⁵:η¹-MeOCH₂CH₂C₉H₅SiMe₃)₂Yb^II (7), (η⁵:η¹-MeOCH₂CH₂C₉H₆)₂Yb^II (8) and the corresponding europium(II) complexes [η⁵:η¹-Me₂Si(MeOCH₂CH₂C₉H₅)(NHBu-t)]₂Eu^II (9), (η⁵:η¹-MeOCH₂CH₂C₉H₅SiMe₃)₂Eu^II (10) and (η⁵:η¹-MeOCH₂CH₂C₉H₆)₂Eu^II (11) in moderate to good yield. In contrast, interaction of the corresponding indene compounds 1, 2 or 3 with the lanthanide amides [(Me₃Si)₂N]₃Ln (Ln = Yb, Eu) was not observed, while addition of 0.5 equiv. of anhydrous LiCl to the corresponding reaction mixture produced, after workup, the corresponding ytterbium(II) or europium(II) complexes. All the new compounds were fully characterized by spectroscopic and elemental analyses. The structures of complexes 7, 9 and 10 were determined by single-crystal X-ray analyses. The catalytic activity of all the ytterbium(II) and europium(II) complexes on MMA polymerization was examined. It was found that all the ytterbium(II) and europium(II) complexes can function as single-component MMA polymerization catalysts. The temperature, solvent and ligand effects on the catalytic activity were studied.