Homoleptic rare-earth metal complexes containing Ln-C σ-bonds.
Homoleptic rare-earth metal complexes containing Ln-C σ-bonds.
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DOI：
10.1021/cr1001194
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发表时间：
2010-09
期刊：
影响因子：
62.1
通讯作者：
Melanie Zimmermann;R. Anwander
中科院分区：
文献类型：
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作者：
Melanie Zimmermann;R. Anwander
分别使用硼酸盐试剂[Ph3C][B(C6F5)4]和[PhNMe2H][B(C6F5)4]的离子可产生高活性的聚合催化剂(表4)。Sc双(烷基)配合物51Sc对间规均聚表现出良好的活性(活性为1.36×104(KgPS)/(MolSc H)；mw/mN)1.37；配合物51、53和54适合于一系列单体的共聚和共聚。约束几何络合物将环戊二烯基辅基配体结合到(侧基)给电子体的螯合阵列中，从而获得重要的CP衍生物。自从Bercaw基团最初引入以来，连接的氨基-环戊二烯(CP)配体已发展成为第4族金属聚合催化剂中用途最广泛的配体之一。235基于这种配体的催化剂提供了一个受限的配体环境，但预计对空间要求高的单体的催化活性高于茂金属。氨基环戊二烯前体与Ln(CH2SiMe3)3(THF)x(Jthf)通过烷烃消除反应以类似于方案30所示的方式反应。由于所得配体的双阴离子性质，在所得化合物中只保留了一个[CH2SiMe3]配体，这允许进一步的衍生化(图11)。在Ph_3SiH或H_2存在下，配合物66-73形成二聚体配合物176,177,204,236，表现出很高的催化烯烃硅氢加成反应的潜力。226,237,238的催化活性和立体选择性受环戊二烯基和氨基官能团之间的连接物的长度和氨基取代基的影响。当用等摩尔量的[Ph3C][B(C6F5)4]活化时，这些化合物聚合乙烯和异戊二烯，区域特定地产生具有丰富的全同立构的立体微结构和相对较窄的分子量分布(Mw/Mn)1.8的3，4-聚异戊二烯。222发现化合物67Y引发了极性单体丙烯酸叔丁酯和丙烯腈的聚合，但产生了无规聚合产物(见表5)。中性含氮和含氧配体的络合物虽然早期的有机稀土金属化学工作主要是由不同取代和修饰的环戊二烯型配体支撑的络合物，但这些配体组固有的局限性引发了替代辅助配体的发展。特别是在过去的15年里，先进的配体设计使人们能够在非环戊二烯配体环境下获得各种各样的稀土金属配合物。由于稀土金属离子的Lewis酸性，基于硬施主元素氧和氮的配体是最常用的，但也有一些值得注意的例外。为了避免配体的重新分布，多齿配体通常受到青睐。由于稀土金属阳离子在+3氧化态(除Eu(II)、Sm(II)、Yb(II)和Ce(IV)外)是不变的，因此中性、单阴离子或双阴离子配位体是最理想的。表4.半夹心配合物(Cp)Ln(CH2SiMe3)2(给体)x化合物的进一步应用参考文献50[CH2SiMe3]交换反应205-209形成单(阳离子)交替的乙烯-降冰片烯共聚
ion using borate reagents [Ph3C][B(C6F5)4] and [PhNMe2H][B(C6F5)4], respectively, results in highly active polymerization catalysts (Table 4). Scandium bis(alkyl) complex 51Sc shows excellent activity for the syndiospecific styrene homopolymerization (activity, 1.36 × 104 (kg PS)/ (mol Sc h); Mw/Mn ) 1.37), and complexes 51, 53, and 54 proved suitable for the coand terpolymerization of a series of monomers.204,206,210-225 8.2.3. Constraint Geometry Complexes Incorporation of the cyclopentadienyl ancillary ligand into a chelate array of (pendant) donor functionalities gives access to prominent Cp derivatives. Since the original introduction by the Bercaw group, the linked amido-cyclopentadienyl (Cp) ligand has advanced to be one of the most versatile ligands for group 4 metal polymerization catalysts.235 Catalysts based on this type of ligand provide a constrained ligand environment but are anticipated to be more active toward sterically demanding monomers than metallocenes. Aminecyclopentadiene proligands react with Ln(CH2SiMe3)3(thf)x (Jthf) according to an alkane-elimination reaction in a similar manner as shown in Scheme 30. Because of the dianionic nature of the resulting ligand, only one [CH2SiMe3] ligand is retained in the resulting compounds, which allows for further derivatization (Chart 11). In the presence of Ph3SiH or H2, complexes 66-73 form dimeric hydrido complexes,176,177,204,236 showing high potential in the catalytic hydrosilylation of olefins.226,237,238 Catalytic activities and stereoselectivities are hereby influenced by the length of the linker between the cyclopentadienyl and the amido-functionality and the substituents at the amidonitrogen.237 Remarkable catalytic activity was observed for complexes 68cyclohexyl. Upon activation with equimolar amounts of [Ph3C][B(C6F5)4], such compounds polymerized ethylene and isoprene, regiospecifically yielding 3,4-polyisoprene with isotactic-rich stereo microstructures and relatively narrow molecular weight distribution (Mw/Mn ) 1.8).222 Complex 67Y was found to initiate the polymerization of the polar monomers tert-butyl acrylate and acrylonitrile, however, yielding atactic polymeric products (see Table 5).204 8.2.4. Complexes with Neutral Nitrogenand Oxygen-Based Ligands While early work in organorare-earth metal chemistry was dominated by complexes supported by cyclopentadienyl-type ligands of varying substitution and modification, the limitations inherent to these ligand sets triggered the development of alternative ancillary ligands. Particularly in the past 15 years, advanced ligand design gave access to a wide variety of rare-earth metal complexes supported by noncyclopentadienyl ligand environments. Because of the Lewis acidic nature of the rare-earth metal ions, ligands based on the hard donor elements oxygen and nitrogen are most commonly used, while some notable exceptions have been reported. To avoid ligand redistribution, multidentate ligands are generally favored. Since rare-earth metal cations are invariable in the +3 oxidation state (except Eu(II), Sm(II), Yb(II), and Ce(IV)), neutral, monoanionic, or dianionic ligand sets are the most desirable. Table 4. Further Applications of Half-Sandwich Complexes (Cp)Ln(CH2SiMe3)2(donor)x compound further application ref 50 [CH2SiMe3] exchange reactions 205-209 formation of mono(cations) alternating ethylene-norbornene copolymerization