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.