Synthesis, Reaction Of Mono(Arylamido) Rare Earth Metal Bis(Amide) Complexes And Their Catalytic Performance In Polymerization

A series of neutral rare earth metal bis(amide) complexes bearing a monodentate arylamido ancillary ligand were synthesized and well-characterized. These complexes could serve as efficient initiators for the ring-opening polymerization of L-laclide as well as cationic catalyst precursors for isoprene polymerization, in which the heterotrinuclear Ln/Al alkyl complexes were presumed as the active species in the polymerization.1. Salt metathesis reaction of LnCl3 with 1 equivalent of [2,6-iPr2C6H3N(SiMe3)]Li, followed by the introduction of two equivalents LiN(SiHMe2)2 in THF at room temperature, afforded a series of neutral rare earth metal bis(amide) complexes [2,6-iPr2C6H3N(SiMe3)]Ln[N(SiHMe2)2]2(THF) (Ln= Sc (1), Y (2), Lu (3), La (4)). These complexes were characterized by 1H NMR,13C NMR, FT-IR spectroscopy and elemental analysis. Complexes 1-3 were also characterized by X-ray crystallography. Single crystal structural determination of 1-3 revealed that the metal centers are four-coordinated to form a distorted tetrahedron.2. Reaction of [2,6-iPr2C6H3N(SiMe3)]Ln[N(SiHMe2)2]2(THF) with excess AlMe3 in 1:6 molar ratio in toluene afforded the mo no (arylamido) ligated Ln/Al heterotrinuclear alkyl complexes [2,6-iPr2C6H3N(SiMe3)]Ln[(μ-Me)2AlMe2]2 (Ln= Y (5), Lu (6), La (7)) via amide-alkyl exchange. These complexes were characterized by 1H NMR,13C NMR, FT-IR spectroscopy and elemental analysis. Complexes 5 and 6 were also characterized by X-ray crystallography. Single crystal structural determination of 5 and 6 revealed that the rare earth metal centers are five-coordinated to form a distorted rectangular pyramid.3. Neutral mono(arylamido) rare earth metal bis(amide) complexes 1-4 could initiate efficiently the ring-opening polymerization of L-lactide at 60 ℃ in a controlled fashion. On activated with one equivalent of [Ph3C][B(C6F5)4], complex 3 and 4 were active for isoprene polymerization. The ternary catalytic systems of 1-4/[Ph3C][B(C6F5)4]/AlR3 (R= AlMe3, AliBu3) could catalyze cis-1,4-selective polymerization of isoprene to afford high molecular weight polymer with narrow molecular weight distuibution. The active species were postulated to be cationic mono(arylamido) Ln/Al heterotrinuclear methyl complexes. The polymers were characterized by 1HNMR spectroscopy and GPC.