Rare-Earth-Metal–Hydrocarbyl Complexes Bearing Linked Cyclopentadienyl or Fluorenyl Ligands: Synthesis, Catalyzed Styrene Polymerization, and Structure–Reactivity Relationship
作者:Zhongbao Jian ,Dongmei Cui and Zhaomin Hou
关键字:cyclopentadienyl ligands, hydrocarbyl complexes, ligand effects, polymerization, rare-earth metals
A series of rare‐earth‐metal–hydrocarbyl complexes bearing N‐type functionalized cyclopentadienyl (Cp) and fluorenyl (Flu) ligands were facilely synthesized. Treatment of [Y(CH2SiMe3)3(thf)2] with equimolar amount of the electron‐donating aminophenyl‐Cp ligand C5Me4H‐C6H4o‐NMe2afforded the corresponding binuclear monoalkyl complex [({C5Me4‐C6H4o‐NMe(μ‐CH2)}Y{CH2SiMe3})2] (1 a) via alkyl abstraction and CH activation of the NMe2 group. The lutetium bis(allyl) complex [(C5Me4‐C6H4o‐NMe2)Lu(η3‐C3H5)2] (2 b), which contained an electron‐donating aminophenyl‐Cp ligand, was isolated from the sequential metathesis reactions of LuCl3 with (C5Me4‐C6H4o‐NMe2)Li (1 equiv) and C3H5MgCl (2 equiv). Following a similar procedure, the yttrium‐ and scandium–bis(allyl) complexes, [(C5Me4‐C5H4N)Ln(η3‐C3H5)2] (Ln=Y (3 a), Sc (3 b)), which also contained electron‐withdrawing pyridyl‐Cp ligands, were also obtained selectively. Deprotonation of the bulky pyridyl‐Flu ligand (C13H9‐C5H4N) by [Ln(CH2SiMe3)3(thf)2] generated the rare‐earth‐metal–dialkyl complexes, [(η3‐C13H8‐C5H4N)Ln(CH2SiMe3)2(thf)] (Ln=Y (4 a), Sc (4 b), Lu (4 c)), in which an unusual asymmetric η3‐allyl bonding mode of Flu moiety was observed. Switching to the bidentate yttrium–trisalkyl complex [Y(CH2C6H4o‐NMe2)3], the same reaction conditions afforded the corresponding yttrium bis(aminobenzyl) complex [(η3‐C13H8‐C5H4N)Y(CH2C6H4o‐NMe2)2] (5). Complexes 15 were fully characterized by 1H and 13C NMR and X‐ray spectroscopy, and by elemental analysis. In the presence of both [Ph3C][B(C6F5)4] and AliBu3, the electron‐donating aminophenyl‐Cp‐based complexes 1 and 2 did not show any activity towards styrene polymerization. In striking contrast, upon activation with [Ph3C][B(C6F5)4] only, the electron‐withdrawing pyridyl‐Cp‐based complexes 3, in particular scandium complex 3 b, exhibited outstanding activitiy to give perfectly syndiotactic (rrrr >99 %) polystyrene, whereas their bulky pyridyl‐Flu analogues (4 and 5) in combination with [Ph3C][B(C6F5)4] and AliBu3displayed much‐lower activity to afford syndiotactic‐enriched polystyrene.