Homolysis of the Ln–N bond: Synthesis, characterization and catalytic activity of organolanthanide(II) complexes with furfuryl- and tetrahydrofurfuryl-functionalized indenyl ligands

A series of new organolanthanide(II) complexes with furfuryl- and tetrahydrofurfuryl-functionalized indenyl ligands were synthesized via one-electron reductive elimination reaction. Treatments of [(Me3Si)2N]3LnIII(μ-Cl)Li(THF)3 (Ln = Yb, Eu) with 2 equiv. of C4H7OCH2C9H7 (1) or C4H3OCH2C9H7 (2), respectively in toluene at moderate high temperatures produced, after workup, the corresponding organolanthanide(II) complexes with formula [η5:η1-(C4H7OCH2C9H6)]2LnII (Ln = Yb (5), Ln = Eu (6)) and [η5:η1-(C4H3OCH2C9H6)]2LnII (Ln = Yb (7), Ln = Eu (8)) in reasonable to good yields. Treatments of [(Me3Si)2N]3LnIII(μ-Cl)Li(THF)3 (Ln = Yb, Eu) with 2 equiv. of C4H7OCH2C9H6SiMe3 (3) or C4H3OCH2C9H6SiMe3 (4), respectively, in toluene at moderate high temperatures afforded, after workup, the corresponding organolanthanide(II) complexes with formula [η5:η1-(C4H7OCH2C9H5SiMe3)]2LnII (Ln = Yb (9), Ln = Eu (10)) and[η5:η1-(C4H3OCH2C9H5SiMe3)]2LnII (Ln = Yb (11), Ln = Eu (12)) in good to high yields. All the compounds were fully characterized by spectroscopic methods and elemental analyses. The structure of complex 9 was additionally determined by single-crystal X-ray analyses. Studies on the catalytic activities of complexes showed that the complexes having silyl group functionalized indenyl ligands have high catalytic activities on ε-caprolactone polymerization. The temperatures, substituted groups on the indenyl ligands of the complexes, and solvents effects on the catalytic activities of the complexes were examined.

Graphical abstractA series of new organolanthanide(II) complexes with general formula [η5:η1-(C4H7OCH2C9H5R)]2LnII and [η5:η1-(C4H3OCH2C9H5R)]2LnII (Ln = Yb, Eu; R = Me3Si, H) were synthesized and characterized. Studies showed that the complexes with both trimethylsilyl and furfuryl- or tetrahydrofurfuryl-functionalized groups on indenyl ligands have high catalytic activities on ring-opening polymerization of ε-caprolactone.Figure optionsDownload full-size imageDownload as PowerPoint slide