Synthesis of linked half sandwich rare-earth metalchlorido and borohydrido complexes and theircatalytic behavior towards MMA polymerization
作者：Zhongbao Jian, Wei Zhao, Xinli Liu, Xuesi Chen, Tao Tang, and Dongmei Cui
关键字：rare-earth metal; multiple bridges; borohydrido; activation; catalytic
论文来源：期刊
具体来源：http://pubs.rsc.org/en/content/articlepdf/2010/dt/c001824d
发表时间：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 molSc?1 h?1)
and afforded syndiotactic PMMA (rr = 75%) at low polymerization temperature
(20 °C) in THF.
