Reaction of the amido-bridged zirconium complex (CpSiMe2NSiMe2Cp)ZrCH3 (1) (Cp = C5H4) with half an equivalent of B(C6F5)3 or Ph3CB(C6F5)4 afforded the binuclear zirconium complexes [(CpSiMe2NSiMe2Cp)Zr)2(μ-CH3)][RB(C6F5)3] (2a, R = CH3, 2b, R = C6F5) with a methyl group as the bridge between the two zirconium atoms. In the presence of one equivalent of B(C6F5)3 or Ph3C(C6F5)4, 1 was transformed to the zwitterionic complexes [(CpSiMe2NSiMe2Cp)Zr][RB(C6F5)3] (3a, R = CH3, 3b, R = C6F5) which are free of a metal-bound σ-alkyl ligand. 2b is stable with Me3Al while 3b combined with Me3Al to form a hetero-binuclear complex [(CpSiMe2NSiMe2Cp)Zr(μ-CH3)]Al(CH3)2][B(C6F5)4] (4) as shown by NMR spectroscopy at room temperature. Treatment of 2a or 3a with an excess of Me3Al led to (CpSiMe2NSiMe2Cp)Zr(C6F5) (5) through a group exchange process. 2b, 3a and 5 have been characterized by X-ray diffraction studies. 2a, 2b, 3a and 3b were highly active catalysts for ethylene polymerization and copolymerization with 1-octene in the presence of trialkylaluminium, but the binuclear zirconium complexes (2a and 2b) showed higher activities than their mononuclear counterparts 3a and 3b. Polymerization activities varied with the trialkylaluminiums and increased with the trialkylaluminium concentration applied in the system. The product existed mainly in the form of Al(PE)3 with polymeric chains, and its molecular weight and distribution were greatly influenced by the type and amount of trialkylaluminium applied in the catalytic system.
酰胺桥
锆配合物 (CpSiMe2NSiMe2Cp)Zr (1) (Cp =
C5H4) 与半当量的 B(
C6F5)3 或 Ph3CB( )4 反应,得到双核
锆配合物 [(CpSiMe2NSiMe2Cp)Zr)2(μ -
CH3)][RB( )3] (2a, R = , 2b, R = ),其中甲基作为两个
锆原子之间的桥。在一当量的 B( )3 或 Ph3C( )4 存在下,1 转化为两性离子配合物 [(CpSiMe2NSiMe2Cp)Zr][RB( )3] (3a, R = , 3b, R = ),不含
金属结合的σ-烷基
配体。 2b 与 Me3Al 稳定,而 3b 与 Me3Al 结合形成异双核络合物 [(CpSiMe2NSiMe2Cp)Zr(μ- )]Al( )2][B( )4] (4),如 NMR 光谱所示室温。用过量的 Me3Al 处理 2a 或 3a 通过基团交换过程得到 (CpSiMe2NSiMe2Cp)Zr( ) (5)。图2b、3a和5已经通过X射线衍射研究进行了表征。 2a、2b、3a和3b是在三烷基铝存在下
乙烯聚合和与1-
辛烯共聚的高活性催化剂,但双核
锆配合物(2a和2b)比单核对应物3a和3b表现出更高的活性。聚合活性随三烷基铝的不同而变化,并且随着系统中应用的三烷基铝浓度的增加而增加。产物主要以具有聚合链的Al(PE)3形式存在,其分子量和分布受催化体系中三烷基铝的种类和用量影响较大。