Homogeneous ethylene-polymerization catalysts based on alkyl cations of the rare-earth metals: Are dicationic mono(alkyl) complexes the active species?
Homogeneous ethylene-polymerization catalysts based on alkyl cations of the rare-earth metals: Are dicationic mono(alkyl) complexes the active species?
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DOI：
10.1002/anie.200352532
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发表时间：
2003-01-01
影响因子：
16.6
通讯作者：
Okuda, J
中科院分区：
文献类型：
--
作者：
Arndt, S;Spaniol, TP;Okuda, J
第4族金属的阳离子烷基络合物，例如烷基锆阳离子，目前在均相烯烃聚合反应中作为单位点催化剂发挥关键作用。[1]第一个阳离子烷基稀土金属配合物[La（η5-C5 Me 5）{CH（SiMe 3）2}（thf）x]+[BPh 4] n（x= 0或3）在1992年报道，[2a]并且从那时起，只有一个报道有证据表明这种配合物，钪二甲基阳离子，聚合乙烯。[2b]许多由单阴离子辅助非配体L支撑的稀土金属[Ln（L）R]+的阳离子烷基络合物，例如酰胺基官能化的三氮杂环壬烷[3]，β-二酮亚胺[4]或苯甲脒[5]，被推测也催化乙烯聚合。我们报道了热敏性三（三甲基硅甲基）配合物[Ln（CH 2SiMe 3）3（thf）2]（Ln= Lu，Y）[6]通过与BPh 3反应可以转化为稳定的单阳离子双（烷基）配合物[Ln（CH 2Si-Me 3）2（thf）x]+。[7]本文报道了不含任何辅助配体L的三烷基配合物[Ln（CH_2SiMe_3）_3（thf）_2]可作为高活性催化剂的前体用于乙烯均相聚合。有证据表明，活性物种是双阳离子[Ln（CH 2SiMe 3）（solv）z] 2+，其通过二烷基单阳离子[Ln（CH 2SiMe 3）2（solv）y]+质子化[Ln（CH 2SiMe 3）3（thf）2]而形成。烷基配合物[Ln（CH 2Si-Me 3）3（thf）2]（Ln= Tm，Er，Y，Ho，Dy，Tb）的甲苯溶液在AliBu 3存在下用布朗斯台德酸[NMe 2 HPh][B（C6 F5）4]活化后有效地催化乙烯聚合。在5巴乙烯压力下短时间运行（10分钟）后，生产出分子量Mn= 3500-45000和多分散性Mw/Mn= 2-6的线性聚乙烯，其活性高达899千克摩尔/小时/巴（表1）。如图1所示，催化剂的性能可以通过选择稀土金属来调节，因为活性与催化剂的活性相关。
Cationic alkyl complexes of Group 4 metals, for example, alkyl zirconocenium ions, currently play a pivotal role as single-site catalysts in homogeneous olefin-polymerization reactions.[1] The first cationic alkyl rare earth metal complex [La (η5-C5Me5){CH (SiMe3) 2}(thf) x]+[BPh4] À (x= 0 or 3) was reported in 1992,[2a] and since then, there has only been one report with evidence that such a complex, a scandium dimethyl cation, polymerizes ethylene.[2b] A number of cationic alkyl complexes of the rare-earth metals [Ln (L) R]+ supported by monoanionic ancillary noncyclopentadienyl ligands L, such as the amido-functionalized triazacyclononane,[3] β-diketiminate,[4] or benzamidinate [5] were surmised to also catalyze ethylene polymerization. We reported that the thermally sensitive tris (trimethylsilylmethyl) complexes [Ln (CH2SiMe3) 3 (thf) 2](Ln= Lu, Y)[6] can be transformed into robust monocationic bis (alkyl) complexes [Ln (CH2Si-Me3) 2 (thf) x]+ by the reaction with BPh3.[7] Herein we report that the tris (alkyl) complexes [Ln (CH2SiMe3) 3 (thf) 2] without any ancillary ligand L can act as precursors for highly active catalysts for homogeneous ethylene polymerization. There is evidence that the active species are the dications [Ln (CH2Si-Me3)(solv) z] 2+, which are formed by the protonolysis of [Ln (CH2SiMe3) 3 (thf) 2] via the dialkyl monocations [Ln (CH2SiMe3) 2 (solv) y]+. Toluene solutions of the alkyl complexes [Ln (CH2Si-Me3) 3 (thf) 2](Ln= Tm, Er, Y, Ho, Dy, Tb) efficiently catalyze ethylene polymerization upon activation with the Brønsted acid [NMe2HPh][B (C6F5) 4] in the presence of AliBu3. After short run times (10 min) at 5 bar of ethylene pressure, linear polyethylenes with molecular weights Mn= 3500–45000 and polydispersities Mw/Mn= 2–6 were produced with activities up to 899kgmolÀ1 hÀ1 barÀ1(Table1). As illustrated in Figure 1, the catalyst performance can be adjusted by the choice of the rare-earth metal as the activity is well correlated