Synthesis of double silylene‐bridged binuclear zirconium complexes and their use as catalysts for olefin polymerization

Abstract

New double silylene‐bridged binuclear zirconium complexes [(η5‐RC5H4)ZrCl2]2[μ,μ‐(SiMe2)2(η5‐C5H3)2] [R = H (1), Me (2), nPr (3), iPr (4), nBu (5), allyl (6), 3‐butenyl (7), benzyl (8), PhCH2CH2 (9), MeOCH2CH2 (10)] were synthesized by the reaction of (η5‐RC5H4)ZrCl3·DME with [μ,μ‐(SiMe2)2(η5‐C5H3)2]2− (L2−) in THF, and they were all well characterized by 1H NMR, MS, IR, and EA. The binuclear structure of Complex 3 was further confirmed by X‐ray diffraction, where the two zirconium centers are located trans relative to the bridging [μ,μ‐(SiMe2)2(η5‐C5H3)2] moiety. When activated with methylaluminoxane (MAO), this series of zirconium complexes are highly active catalysts for the polymerization of ethylene even under very low molar ratio of Al/Zr (Complex 7, 5.41 × 105 g‐PE/mol‐Zr·h, Al/Zr = 50) and linear polyethylenes (PEs) with broad molecular weight distribution (MWD, Mw/Mn = 7.31–27.6) was obtained. The copolymerization experiments indicate that these complexes are also very efficient in the incorporation of 1‐hexene into the growing PE chain in the presence of MAO (Complex 6, 3.59 × 106 g‐PE/mol‐Zr·h; 1‐hexene content, 3.65%). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4901–4913, 2007

Synthesis of double silylene‐bridged binuclear metallocenes and their cooperation effect during ethylene polymerization and ethylene/1‐hexene copolymerization

“…The parent molecular ion peaks of complexes 1-6 could not be detected in all of the Mass spectra (EI, 70 eV). The most important character in the Mass spectra is that the ion peak corresponding to the mononuclear fragment was observed in all cases, in the same manner as Huang 12 found for the double-bridged binuclear zirconium complexes.…”

“…It is found that catalytic activities of binuclear zirconium complexes are higher than that of Cp 2 ZrCl 2 under the identical conditions (a similar situation was also found for titanium complexes), and the activities of complex 1 exceed 3.86 Â 10 6 g-PE/mol-M h when the ratio of Al/Zr ¼ 500. Additionally, these complexes/MAO systems keep high activity even at low ratio of Al/Zr just as Huang 12 found. It is noteworthy that despite the differences in substituents on the bridge Cp, alkyl, allyl, or …”

“…On the other hand, when the substituent group is a potentially weakly coordinating group (Complex 2, 3, 4), the catalytic activity is higher than that of the corresponding alkyl(R ¼ alkyl). We discovered this in our former work 12 and attributed it to the coordination between the allyl and activated center metal and the resulting improvement in the stability of the catalyst. This postulate is supported by the polymerization results showing the effect of polymerization time on catalyst activity (see Table II).…”

“…Among these types of complexes, the double Me 2 Si bridged bisCp metal complexes, including mononuclear and binuclear types have been studied and summarized in Huang's article. 12 They [12][13][14][15] found that single-bridged/ 2 ], and introduce a series of different substituents on Cp ring. They then studied their catalytic behavior for ethylene polymerization and ethylene/ 1-hexene copolymerization in the presence of MAO.…”

Asymmetric binuclear metallocene complexes and their application for olefin polymerization

“…In the last decade, our group found that single‐bridged/double‐bridged hetero‐binuclear or homo‐binuclear titanium complexes with different substituted Cp ring gave excellent results on the olefin polymerization. In order to increase the stereo rigidity of the complexes, we have designed and synthesized binuclear zirconium complexes with double silylene‐bridge and introduced a series of different substituents on Cp ring, and studied their catalytic behavior for ethylene polymerization and ethylene/1‐hexene copolymerization in the presence of MAO. It is found that all the binuclear zirconium complexes are effective catalysts not only for ethylene polymerization even under low ratio of Al/Zr (5.41 × 10 5 g‐PE/mol‐Zr·h, Al/Zr = 50), but also for ethylene/1‐hexene copolymerization (3.59 × 10 6 g‐PE/mol‐Zr·h; 1‐hexene content, 3.65% mol); polymers with broader PD ( M w/ M n = 7.31–27.6) were obtained.…”