Synthesis and structural characterization of {[Me2Si(C5Me4)2]Zr(η2-C2H4)H}2Mg:: An ansa-zirconocene ethylene-hydride complex
Synthesis and structural characterization of {[Me2Si(C5Me4)2]Zr(η2-C2H4)H}2Mg:: An ansa-zirconocene ethylene-hydride complex
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DOI：
10.1021/ja980813b
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发表时间：
1998-06-17
影响因子：
15
通讯作者：
Parkin, G
中科院分区：
文献类型：
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作者：
Lee, H;Hascall, T;Parkin, G
茂锆烯烃配合物长期以来一直被用作各种重要合成转化中的关键中间体。例如，二茂锆催化的碳镁化 1 涉及通过有机镁试剂对烯烃进行烷基化，通常认为是通过 [CpR] 2Zr (CH2dCHR) 发生，该烯烃络合物是通过 [CpR] 2ZrCl2 与 RCH2CH2MgX 反应生成的。同样，二茂锆烯烃氢化物和烷基物质是催化烯烃加氢和聚合的重要中间体。 3 此外，烯烃-氢化物络合物被认为是在氢化锆化4 和聚合过程中导致烷基异构化的可能中间体。 5-7 然而，尽管茂锆烯烃-氢化物配合物具有重要意义，但尚未对其进行分离和结构表征。在本文中，我们描述了第一个具有结构特征的二茂锆配合物，即{[Me2Si (C5Me4) 2] Zr (η2-C2H4) H} 2Mg。卤化锆衍生物[CpR] 2ZrX2 与烷基化剂（例如RMgX、RLi、R3Al 和甲基铝氧烷）的反应已得到广泛研究。有趣的是，尽管这些反应可能极其复杂，8 但它们仍然为有机合成9 和烯烃聚合提供了重要的试剂。 3 由于 ansa 衍生物在上述应用中也很普遍，我们选择研究 ansa 络合物 [Me2Si (C5Me4) 2] ZrBr2 10 与格氏试剂的反应（方案 1）。值得注意的是，[Me2Si (C5Me4) 2] ZrBr2 与 MeMgBr 的反应产生二甲基衍生物 [Me2Si (C5Me4) 2] ZrMe2，11 与 EtMgBr 的相应反应产生烯烃-氢化物络合物 {[Me2Si (C5-Me4) 2] Zr (η2-C2H4) H} 2Mg。后一种络合物也可以通过将(CH2dCH) 2Mg 的乙烯基插入到{[Me2Si(C5Me4) 2] Zr(H)(μ-H)} 2 的Zr-H键中来获得(方案1)。 11 通过 X 射线衍射测定了固态 {[Me2Si (C5Me4) 2] Zr (η2-C2H4) H} 2-Mg 的分子结构（图 1），12 其中 {[Me2Si (C5Me4) 2] Zr (η2-C2H4) H}-片段表现出弯曲茂金属衍生物的预期几何形状。 13 此外，衍射研究表明，其中两个 {[Me2Si (C5Me4) 2] Zr (η2-C2H4) H}-单元通过 Mg2+ 中心连接，该中心主要与氢化锆配体和乙烯配体的中心亚甲基相互作用；因此，镁采用伪四面体配位。 14, 15 推测由于这种相互作用，锆-烯烃键合是不对称的，d (Zr-Ccent)) 2.43 Å 和 d (Zr-Clatt)) 2.26 Å。 16-18 同样明显的是，CC 键长为 1.48 Å，{[Me2-
Zirconocene olefin complexes have long been invoked as critical intermediates in a variety of synthetically important transformations. For example, zirconocene-catalyzed carbomagnesiation, 1 which involves the alkylation of an olefin by organomagnesium reagents, is commonly considered to occur via an olefin complex [CpR] 2Zr (CH2dCHR) that is generated by reaction of [CpR] 2ZrCl2 with RCH2CH2MgX. Likewise, zirconocene olefin-hydride and-alkyl species are important intermediates in catalytic olefin hydrogenation2 and polymerization. 3 Furthermore, olefin-hydride complexes are viewed to be the likely intermediates responsible for alkyl group isomerization during hydrozirconation4 and polymerization. 5-7 Despite their significance, however, zirconocene olefin-hydride complexes have not been isolated and structurally characterized. In this paper, we describe the first structurally characterized zirconocene ethylenehydride complex, namely {[Me2Si (C5Me4) 2] Zr (η2-C2H4) H} 2Mg. The reactions of zirconocene halide derivatives [CpR] 2ZrX2 with alkylating agents (eg, RMgX, RLi, R3Al, and methylalumoxane) have been widely studied. Interestingly, even though these reactions may be surprisingly complex, 8 they nevertheless provide important reagents for organic synthesis9 and catalysts for olefin polymerization. 3 Since ansa derivatives are also prevalent in the aforementioned applications, we have elected to investigate the reactions of the ansa complex [Me2Si (C5Me4) 2] ZrBr2 10 with Grignard reagents (Scheme 1). Significantly, whereas the reaction of [Me2Si (C5Me4) 2] ZrBr2 with MeMgBr yields the dimethyl derivative [Me2Si (C5Me4) 2] ZrMe2, 11 the corresponding reaction with EtMgBr yields the olefin-hydride complex {[Me2Si (C5-Me4) 2] Zr (η2-C2H4) H} 2Mg. The latter complex may also be obtained by insertion of the vinyl group of (CH2dCH) 2Mg into the Zr-H bond of {[Me2Si (C5Me4) 2] Zr (H)(µ-H)} 2 (Scheme 1). 11 The molecular structure of {[Me2Si (C5Me4) 2] Zr (η2-C2H4) H} 2-Mg has been determined in the solid state by X-ray diffraction (Figure 1), 12 with the {[Me2Si (C5Me4) 2] Zr (η2-C2H4) H}-fragment exhibiting the expected geometry for a bent metallocene derivative. 13 Furthermore, the diffraction study demonstrates that two of these {[Me2Si (C5Me4) 2] Zr (η2-C2H4) H}-units are linked via a Mg2+ center, which interacts principally with the zirconium hydride ligands and the central methylene groups of the ethylene ligands; as such, the magnesium adopts a pseudo-tetrahedral coordination. 14, 15 Presumably as a result of this interaction, the zirconium-olefin bonding is asymmetric, with d (Zr-Ccent)) 2.43 Å and d (Zr-Clatt)) 2.26 Å. 16-18 It is also evident that, with a CC bond length of 1.48 Å, the [Zr (η2-C2H4)] moiety of {[Me2-