Indenyl abstraction versus alkyl abstraction of [(Indenyl)ScR2(thf)] by [Ph3C] [B(C6F5)4]: aspecific and syndiospecific styrene polymerization.
Indenyl abstraction versus alkyl abstraction of [(Indenyl)ScR2(thf)] by [Ph3C] [B(C6F5)4]: aspecific and syndiospecific styrene polymerization.
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DOI：
10.1002/chem.200802220
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发表时间：
2009-01
期刊：
影响因子：
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通讯作者：
Xin Xu;Yao-Quan Chen;Jie Sun
中科院分区：
文献类型：
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作者：
Xin Xu;Yao-Quan Chen;Jie Sun
半世纪前，人们研究了茂金属配合物[Cp2TiCl2] （Cp=环戊二烯基）在AlR3或AlR2Cl活化下的烯烃聚合反应，发现其催化活性较低。19年后，Sinn、Kaminsky和同事发现，使用甲基铝氧烷（MAO）作为活化剂，可以极大地增强[Cp2MR2] （M =Ti和Zr）对烯烃聚合的活性。[2]随后的机理研究表明，IV族茂金属/MAO体系中的活性物质是阳离子茂金属烷基，它们是由MAO对中性茂金属配合物的烷基萃取反应生成的。获得阳离子茂金属烷基的另一种途径是采用定义明确的强路易斯酸，如B ACHTUNGTRENNUNG(C6F5)3，来抽象中性茂金属烷基配合物的烷基。然而，在某些情况下，反离子[R B ACHTUNGTRENNUNG(C6F5)3]通过R桥接与高亲电性阳离子形成“紧密”离子对，与单体配位竞争，导致催化活性下降，特别是在a-烯烃聚合中。为了克服这一问题，研究了含有配位较弱的阴离子[B ACHTUNGTRENNUNG(C6F5)4]的[Ph3C][B ACHTUNGTRENNUNG(C6F5)4]作为活化剂。[Ph3C] +部分是一个很好的烷基或氢化物萃取剂，形成“无害”的副产物Ph3C R，由此产生的“松散”离子对配合物[Cp2MR] +[BACHTUNGTRENNUNG(C6F5)4]通常具有较高的烯烃聚合活性。[5]研究发现，中性稀土金属烷基配合物也可以通过烷基抽离转化为阳离子，所生成的阳离子活性普遍高于中性。例如，[Cp ' scr2achtungtrennung (thf)]/ ACHTUNGTRENNUNG[Ph3C][B ACHTUNGTRENNUNG(C6F5)4] （Cp ' =取代环戊二烯）体系对苯乙烯的共聚合、苯乙烯与乙烯（或异戊二烯）的共聚合以及乙烯与非born ACHTUNGTRENNUNGene的交替共聚具有良好的催化活性，从而制备出一些性能优异的材料。最近，我们制备了一系列单ACHTUNGTRENNUNG（独立基）- sc -二烷基配合物，并研究了它们以[Ph3C][BACHTUNGTRENNUNG(C6F5)4]为活化剂对苯乙烯聚合的反应性。研究发现了一个有趣的现象：[Ph3C][B ACHTUNGTRENNUNG(C6F5)4]不仅是烷基配体，而且是p键的inachtungtrennungenyl配体，由此得到的两种阳离子物种催化苯乙烯聚合，分别得到顺双规聚苯乙烯（sPS）和无规聚苯乙烯（aPS）。在此我们描述这些结果。第一个尝试制备单ACHTUNGTRENNUNG（独立基）- sc -二烷基配合物的配体前体是1,3- bisachtungtrennung（甲基）茚和1,3-双（异丙基）茚。然而，这两种化合物与[Sc ACHTUNGTRENNUNG(CH2SiMe3)3 ACHTUNGTRENNUNG(thf)2]的烷烃消除反应在室温下没有发生，升高反应温度导致Sc -三烷基配合物逐渐分解，没有得到期望的配合物。与烷基取代基相比，SiMe3基团具有较强的吸电子性，[15]，我们希望SiMe3取代基的这一性质能够促进相关配体前体与[ScACHTUNGTRENNUNG(CH2SiMe3)3ACHTUNGTRENNUNG(thf)2]的烷烃消去反应。因此，制备了配体前体1,3-二（三甲基硅基）茚，并对其与[Sc ACHTUNGTRENNUNG(CH2SiMe3)3ACHTUNGTRENNUNG(thf)2]的反应进行了研究。令我们高兴的是，反应成功了，并产生了所需的单ACHTUNGTRENNUNG（独立基）- sc -二烷基配合物。随后，合成了另外7种具有SiMe3取代基的配体前体，这些配体前体与[Sc ACHTUNGTRENNUNG(CH2SiMe3)3 ACHTUNGTRENNUNG(thf)2]反应均得到单ACHTUNGTRENNUNG（独立基）- Sc -二烷基配合物（方案1）。这些Sc配合物通过核磁共振谱（H， C）进行了表征[a]徐旭，陈玉娟，孙军，教授，中国科学院上海有机化学研究所有机金属化学国家重点实验室，上海市200032，传真：（+86）2164166128 E-mail：yaofchen@mail.sioc.ac.cn [b]徐旭。华东理工大学先进材料实验室和精细化工研究所，上海市梅龙路130号，200237（中国）。本文的辅助资料可在WWW上找到：http://dx.doi.org/10.1002/chem.200802220。
The metallocene complex [Cp2TiCl2] (Cp=cyclopentadienyl) was investigated for olefin polymerization upon activation with AlR3 or AlR2Cl half a century ago, and showed low catalytic activity. Nineteen years later, Sinn, Kaminsky, and co-workers found that the use of methylaluminoxane (MAO) as the activator greatly enhanced the activity of [Cp2MR2] (M =Ti and Zr) to olefin polymerization. [2] Subsequent mechanistic studies revealed that the active species in Group IV metallocene/MAO systems are cationic metallocene alkyls, which are generated through a reaction involving an alkyl abstraction of the neutral metallocene complexes by MAO. An alternative route to access the cationic metallocene alkyl species is by employing a well-defined strong Lewis acid, such as B ACHTUNGTRENNUNG(C6F5)3, to abstract the alkyl group of neutral metallocene alkyl complexes. However, in some cases, the counterions [R B ACHTUNGTRENNUNG(C6F5)3] form “tight” ion pairs with the highly electrophilic cations through R bridging and compete with coordination of the monomer, which results in a decrease in catalytic activity, especially in a-olefin polymerization. To overcome this problem, [Ph3C][B ACHTUNGTRENNUNG(C6F5)4], which contains a more weakly coordinating anion [B ACHTUNGTRENNUNG(C6F5)4] , was developed as the activator. The [Ph3C] + moiety is an excellent alkyl or hydride abstractor, forming the “innocent” byproduct Ph3C R, and the resulting “loose” ion pairing complexes [Cp2MR] +[BACHTUNGTRENNUNG(C6F5)4] generally show higher activity for olefin polymerization. 5] It was found that neutral rareearth metal alkyl complexes could also be converted into the cationic species through alkyl abstraction, and the cationic species generated generally show much higher activity than the neutral ones. For example, the [Cp’ScR2ACHTUNGTRENNUNG(thf)]/ ACHTUNGTRENNUNG[Ph3C][B ACHTUNGTRENNUNG(C6F5)4] (Cp’= substituted cyclopentadienyl) systems exhibit good catalytic activities for syndiospecific polymerization of styrene, syndiospecific copolymerization of styrene and ethylene (or isoprene), and alternating copolymerization of ethylene and norborn ACHTUNGTRENNUNGene,[13] producing some materials that have excellent properties. Recently, we prepared a series of mono ACHTUNGTRENNUNG(indenyl)–Sc–dialkyl complexes and studied their reactivity towards styrene polymerization with [Ph3C][BACHTUNGTRENNUNG(C6F5)4] as the activator. The study revealed an interesting observation that [Ph3C][B ACHTUNGTRENNUNG(C6F5)4] abstract not only the alkyl ligand but also the p-bonded indACHTUNGTRENNUNGenyl ligand, and the resulting two types of cationic species catalyze styrene polymerization to give syndiotactic polystyrene (sPS) and atactic PS (aPS), respectively. Herein we describe these results. The first ligand precursors that were tried for preparing mono ACHTUNGTRENNUNG(indenyl)–Sc–dialkyl complexes were 1,3-bisACHTUNGTRENNUNG(methyl)indene and 1,3-bis(isopropyl)indene. However, the alkane elimination reactions of these two compounds with [Sc ACHTUNGTRENNUNG(CH2SiMe3)3 ACHTUNGTRENNUNG(thf)2] did not occur at room temperature, and raising the reaction temperature caused the gradual decomposition of the Sc–trialkyl complexes, giving none of the desired complexes. In comparison with alkyl substituents, the SiMe3 group is relatively electron withdrawing, [15] and we hoped that this property of the SiMe3 substituent would promote the alkane elimination reaction of the related ligand precursor with [ScACHTUNGTRENNUNG(CH2SiMe3)3ACHTUNGTRENNUNG(thf)2]. Therefore, the ligand precursor 1,3-bis(trimethylsilyl)indene was prepared, and its reaction with [Sc ACHTUNGTRENNUNG(CH2SiMe3)3ACHTUNGTRENNUNG(thf)2] was investigated. To our delight, the reaction worked and the desired mono ACHTUNGTRENNUNG(indenyl)–Sc–dialkyl complex was produced. Subsequently, seven other ligand precursors with the SiMe3 substituent were synthesized, and reactions of these ligand precursors with [Sc ACHTUNGTRENNUNG(CH2SiMe3)3 ACHTUNGTRENNUNG(thf)2] all gave the monoACHTUNGTRENNUNG(indenyl)–Sc–dialkyl complexes (Scheme 1). These Sc complexes were characterized by NMR spectroscopy (H, C) [a] X. Xu, Prof. Dr. Y. Chen, J. Sun State Key Laboratory of Organometallic Chemistry Shanghai Institute of Organic Chemistry Chinese Academy of Sciences 354 Fenglin Road, Shanghai 200032 (P.R. China) Fax: (+86) 2164166128 E-mail : yaofchen@mail.sioc.ac.cn [b] X. Xu Laboratory of Advanced Materials and Institute of Fine Chemicals East China University of Science and Technology 130 Meilong Road, Shanghai 200237 (P.R. China) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200802220.