Ligands Dominate Highly Syndioselective Polymerization of Styrene by Using Constrained-geometry-configuration Rare-earth Metal Precursors
writer：Yupeng Pan, Weifeng Rong, Zhongbao Jian, and Dongmei Cui
keywords：constrained-geometry-configuration; rare-earth metal; coordination; syndioselectivity; activation
source：期刊
specific source：http://pubs.acs.org/doi/pdf/10.1021/ma202558g
Issue time：2012年
A
series of novel constrained-geometry-configuration (CGC) rare-earth metal
complexes (RCH2–Py)Ln(CH2SiMe3)2(THF)n (Py
= pyridyl; Ln = Y, n = 1, R = C5Me4 (Cp′)
(1); Ln = Y, n = 1, R = C9H6 (Ind)
(2); Ln = Y, n = 1, R = C13H8 (Flu)
(3a); Ln = Lu, n = 1, R = C13H8 (Flu)
(3b); Ln = Sc,n = 0, R = C13H8 (Flu)
(3c)) have been synthesized by treating rare-earth metal trisalkyls with
PyCH2–Cp′, PyCH2–Ind, and PyCH2–Flu compounds,
respectively, and fully characterized by NMR and X-ray diffraction analyses.
Complexes 1, 2, and 3a–b are
monomeric THF solvates while the scandium complex 3c is
solvent-free, in which all the CGC ligands adopt a η5/κ1bonding
mode via coordination of five carbon atoms from the cyclopentadienyl fragment
and the pyridyl nitrogen atom with the central metals. Upon activation with AliBu3 and
[Ph3C][B(C6F5)4], these complexes
showed different performances toward styrene polymerization. The Cp′CH2–Py
and IndCH2–Py ligated yttrium complexes 1 and 2 showed
very low activity to afford syndiotactic enriched polystyrene. Strikingly, the
bulky FluCH2–Py supported complexes 3a–c displayed
outstanding activities up to 1.56 × 107 g/(molLn·h)
and perfect syndioselectivity (rrrr > 99%), giving high
molecular weight sPS; in particular, thus excellent performance was independent
of the central metal type for the first time. In addition, the relationship of
the ligand structure with the catalytic performances toward specific selective
polymerization of styrene was reasonably revealed by comparison with the other
Flu-based rare-earth metal catalysts reported previously by us. This might open
a new pathway for designing catalysts for specifically selective polymerizations.
