Rare-earth metal bis(silylamide) complexes supported by mono-dentate arylamido ligand: synthesis, reactivity, and catalyst precursors in living cis-1,4-selective polymerization of isoprene

Abstract

The salt metathesis reaction of LnCl₃ with 1 equivalent of arylamido lithium [2,6-ⁱPr₂C₆H₃N(SiMe₃)]Li followed by addition of 2 equivalents of LiN(SiHMe₂)₂ in THF at room temperature obtained neutral mono-arylamido-ligated rare-earth metal bis(silylamide) complexes [2,6-ⁱPr₂C₆H₃N(SiMe₃)]Ln[N(SiHMe₂)₂]₂(THF) (Ln = Y (1), Lu (2), La (3)) in good isolated yields. Treatment of 1–3 with excess AlMe₃ produced the mono(arylamido) Ln/Al heterotrinuclear methyl complexes [2,6-ⁱPr₂C₆H₃N(SiMe₃)]Ln[(μ-Me)₂AlMe₂]₂ (Ln = Y (4), Lu (5), La (6)) via amide–alkyl exchange. All these complexes were well-characterized by elemental analysis, NMR spectroscopy and FT-IR spectroscopy. 2, 4 and 5 were further structurally authenticated by X-ray crystallography. In the presence of [Ph₃C][B(C₆F₅)₄] and AlⁱBu₃, 1–3 were highly active for cis-1,4-selective polymerization of isoprene, whereas 2/[Ph₃C][B(C₆F₅)₄]/AlⁱBu₃ promoted the polymerization in a living fashion.