Stereoselective Polymerization of Styrene with Cationic Scandium Precursors Bearing Quinolyl Aniline Ligands
writer：Dongtao Liu, Yunjie Luo, Wei Gao and Dongmei Cui
keywords：organoborates; cationic complex; precursors; aluminum trialkyls; syndioselectivity
source：期刊
specific source：http://pubs.acs.org/doi/pdf/10.1021/om1000265
Issue time：2010年
The
novel N-R-quinolinyl-8-amino ligands HL1?5 (R = 2,6-Me2C6H3 (HL1),
2,4,6-Me3C6H2 (HL2), 2,6-Et2C6H3 (HL3),
2,6-iPr2C6H3 (HL4),
C6H5 (HL5)) reacted with Sc(CH2SiMe3)3(THF)2 to
afford the well-defined complexes (L1?5)Sc(CH2SiMe3)2(THF)
(1?5), which were fully characterized by NMR spectral and X-ray
diffraction analyses. Complexes 1?3 combined with
organoborates to establish binary systems that exhibited high activity for the
polymerization of styrene, while 4 was less active and 5 was
almost inert. The cationic complex [L1Sc(CH2SiMe3)(DME)2][B(C6F5)4]
(6) was successfully isolated by treatment of 1 with
[PhMe2NH][B(C6F5)4], and represents
probably the structural model of the initiation active species. Remarkably,
upon addition of aluminum trialkyls to the binary systems, distinguished
improvement in catalytic performances was achieved, among which the ternary
system 1/5AliBu3/[Ph3C][B(C6F5)4]
displayed the highest activity (1.56 × 106 g mol?1 h?1)
and syndioselectivity (r = 0.94) via a chain-end control mechanism
governed by the concerted steric effect of the ligand and the aluminum alkyls.
This represents the first non-cyclopentadienyl stabilized rare-earth metal
based catalyst showing both high activity and specific selectivity for the
polymerization of styrene, which might shed new light on designing more
efficient precursors and further investigation of the mechanism for this
polymerization.
