writer：Zhongbao Jian, Wei Zhao, Xinli Liu, Xuesi Chen, Tao Tang, and Dongmei Cui
keywords：rare-earth metal; multiple bridges; borohydrido; activation; catalytic
source：期刊
specific source：http://pubs.rsc.org/en/content/articlepdf/2010/dt/c001824d
Issue time：2010年

A series of rare-earth metal complexes attached by an amino-functionalizedcyclopentadienyl ligand (C₅Me₄H-C₆H₄-o-NMe₂) (1) was prepared. The metathesis reaction of the ligand lithium salt [C₅Me₄-C₆H₄-o-NMe₂]Li with LnCl₃(THF)_n afforded thedichlorido complexes [(C₅Me₄-C₆H₄-o-NMe₂)₂Ln₂Cl₄][LiCl(THF)₂] (Ln = Y (2a), Lu (2b)), which are trinuclear connected by μ₃-Cl and μ₂-Cl multiple bridges. The straightforward metathesis reaction of Ln(BH₄)₃(THF)_n with equimolar [C₅Me₄-C₆H₄-o-NMe₂]Li in THF medium yielded the first linked half sandwich ligand stabilized THF-free rare-earth metal bis(borohydrido) complexes (C₅Me₄-C₆H₄-o-NMe₂)Ln(BH₄)₂ (Ln = Sc(3a), Sm (3b)), respectively. The single component borohydrido complex 3a showed high activity towards the bulk polymerization of methyl methacrylate without specific control, which showed high iso-selectivity (mm = 80%) when the polymerization was performed in benzene medium, and switched to syndio-selectivity (rr = 74% at ?20 °C) in polar THF medium, whilst the metal chlorido species was inert. The binary catalyst system of 3a/MgⁿBu₂ had similar catalytic performances when compared with 3a in THFmedium, but provided enriched syndio-control in benzene solution that was in contrast to the iso-control of 3a. Surprisingly, 3a upon activation with ⁿBuLi displayed an extremely high activity (1.1 × 10⁶ g mol_Sc^?1 h^?1) and afforded syndiotactic PMMA (rr = 75%) at low polymerization temperature (20 °C) in THF.