Synthesis of titanium trichloride complexes of 1,2,3-trisubstituted cyclopentadienyls and their use in styrene polymerization
Introduction
Since Ishihara et al. reported the first preparation of syndiotactic polystyrene (s-PS) using the CpTiCl3/MAO catalyst system [1], [2], a wide variety of new catalytic systems based on titanium or zirconium compounds have been synthesized and studied as s-PS catalyst [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13]. Among those complexes, Cp*TiX3, (indenyl)TiCl3, and (substituted indenyl)TiCl3 derivatives are the most active catalysts. Studies on the mechanism involved in the polymerization of styrene have also been reported [14], [15], [16], [17], [18].
The chemical and physical properties of cyclopentadienyl titanium complexes can be varied over a wide range by modification of the substituents on the cyclopentadienyl ring [19]. Thus, many research groups are involved in the design of ligands to tailor the catalytic activity and product properties. However, a limited range of cyclopentadienyl titanium complexes containing such ligands have been prepared and studied due to the absence of a generalized synthetic method for substituted cyclopentadiene. Recently, Takahashi et al. [20] reported the synthesis of 1,2,3-trisubstituted cyclopentadienes through the reaction of zirconacyclopentene with acid chloride in the presence of a catalytic amount of copper chloride. Several years ago, we reported [21] the general method for preparation of 1,2,3-trisubstituted cyclopentadienyls and their use in the preparation of manganese tricarbonyl and zirconium dichloride derivatives. The method can be easily extended to synthesize 1,2,3-trisubstituted cyclopentadienyl titanium trichlorides. Herein we report the synthesis and characterization of 1,2,3-trisubstituted cyclopentadienyl titanium trichloride and their behavior in styrene polymerization.
Section snippets
General
Reactions were carried out under argon or nitrogen atmosphere using standard Schlenk techniques or in a glove box. Methylaluminoxane (MAO) was purchased from Akzo (6.4 wt.% of Al, MMAO type 4). Chlorotrimethylsilane, dichlorodimethylsilane, and styrene were purified by distillation over CaH2. Hexane and toluene were purified over Na/K alloy under argon. 1H-NMR and 13C-NMR spectra were recorded on a Bruker DPX-300 spectrometer. Elemental analyses were done at the National Centre for
Synthesis
Compound 5 was prepared by treatment of pure anhydrous TiCl4 with 3 in methylene dichloride, a well known and routine technique (Eq. (1)) [3], [5], [6], [7], [8], [9], [10], [11], [19], [22].
Compound 3 was obtained by reaction of 1 with n-BuLi and chlorotrimethylsilane. The overall yield from 1 to 5 was 77%. In the same way, 6 was synthesized with overall yield of 75%. Treatment of cyclopentadienes bearing phenyl group(s) with TiCl4 yielded untraceable black precipitates that might be due to
Supplementary material
Crystallographic data for structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC No. 158012 for compound 14. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (Fax: +44-1223-336033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).
Acknowledgements
This work was supported by the Korea Science and Engineering Foundation (KOSEF) (1999-1-122-001-5) and the KOSEF through the Center for Molecular Catalysis. J.W.H. and H.S. thank the Ministry of Education for the Brain Korea 21 Fellowship.
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*Corresponding author. Tel.: +82-031-2191844; e-mail: [email protected]