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

The salt metathesis reaction of LnCl(3) with 1 equivalent of arylamido lithium [2,6-(Pr2C6H3N)-Pr-i(SiMe3)] Li followed by addition of 2 equivalents of LiN(SiHMe2)(2) in THF at room temperature obtained neutral monoarylamido-ligated rare-earth metal bis(silylamide) complexes [2,6-(Pr2C6H3N)-Pr-i(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-(Pr2C6H3N)-Pr-i(SiMe3)] Ln[(mu-Me)(2)AlMe2](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 (AlBu3)-Bu-i, 1-3 were highly active for cis-1,4-selective polymerization of isoprene, whereas 2/[Ph3C][B(C6F5)(4)]/AliBu(3) promoted the polymerization in a living fashion.