Syndiospecific Living Propylene Polymerization Catalyzed by Titanium Complexes Having Fluorine-Containing Phenoxy-Imine Chelate Ligands
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- 作者：Makoto Mitani ; Rieko Furuyama ; Jun-ichi Mohri ; Junji Saito ; Seiichi Ishii ; Hiroshi Terao ; Takashi Nakano ; Hidetsugu Tanaka ; and Terunori Fujita
- 刊名：Journal of the American Chemical Society
- 出版年：2003
- 出版时间：April 9, 2003
- 年：2003
- 卷：125
- 期：14
- 页码：4293 - 4305
- 全文大小：302K
- 年卷期：v.125,no.14(April 9, 2003)
- ISSN：1520-5126
文摘
The propylene polymerization behavior of a series of Ti complexes featuring fluorine-containingphenoxy-imine chelate ligands is reported. The Ti complexes combined with methylalumoxane (MAO)can be catalysts for living and, at the same time, stereospecific polymerization of propylene at roomtemperature or above. DFT calculations suggest that the attractive interaction between a fluorine ortho tothe imine nitrogen and a 
-hydrogen of a growing polymer chain is responsible for the achievement ofroom-temperature living propylene polymerization. Although the Ti complexes possess C2 symmetry, theyare capable of producing highly syndiotactic polypropylenes. 13C NMR is used to demonstrate that thesyndiotacticity is governed by a chain-end control mechanism and that the polymerization is initiatedexclusively via 1,2-insertion followed by 2,1-insertion as the principal mode of polymerization. 13C NMRspectroscopy also elucidated that the polypropylenes produced with the Ti complexes possess regio-blockstructures. Substitutions on the phenoxy-imine ligands have profound effects on catalytic behavior of theTi complexes. The steric bulk of the substituent ortho to the phenoxy oxygen plays a decisive role in achievinghigh syndioselectivity for the chain-end controlled polymerization. Over a temperature range of 0-50 
C,Ti complex having a trimethylsilyl group ortho to the phenoxy oxygen forms highly syndiotactic, nearlymonodisperse polypropylenes (94-90% rr) with extremely high peak melting temperatures (Tm = 156-149 C). The polymerization behavior of the Ti complexes can be explained well by the recently proposedsite-inversion mechanism for the formation of syndiotactic polypropylene by a Ti complex having a pair offluorine-containing phenoxy-imine ligands.
-hydrogen of a growing polymer chain is responsible for the achievement ofroom-temperature living propylene polymerization. Although the Ti complexes possess C2 symmetry, theyare capable of producing highly syndiotactic polypropylenes. 13C NMR is used to demonstrate that thesyndiotacticity is governed by a chain-end control mechanism and that the polymerization is initiatedexclusively via 1,2-insertion followed by 2,1-insertion as the principal mode of polymerization. 13C NMRspectroscopy also elucidated that the polypropylenes produced with the Ti complexes possess regio-blockstructures. Substitutions on the phenoxy-imine ligands have profound effects on catalytic behavior of theTi complexes. The steric bulk of the substituent ortho to the phenoxy oxygen plays a decisive role in achievinghigh syndioselectivity for the chain-end controlled polymerization. Over a temperature range of 0-50 C,Ti complex having a trimethylsilyl group ortho to the phenoxy oxygen forms highly syndiotactic, nearlymonodisperse polypropylenes (94-90% rr) with extremely high peak melting temperatures (Tm = 156-149 C). The polymerization behavior of the Ti complexes can be explained well by the recently proposedsite-inversion mechanism for the formation of syndiotactic polypropylene by a Ti complex having a pair offluorine-containing phenoxy-imine ligands.