bis(1,2,4-tri-t-butylcyclopentadienyl)cerium bromide | 1160249-67-1

• 英文名称: bis(1,2,4-tri-t-butylcyclopentadienyl)cerium bromide
• 英文别名: [(1,2,4-tri-tert-butylcyclopentadienyl)2CeBr]
• CAS: 1160249-67-1
• 化学式: C₃₄H₅₈BrCe
• 分子量: 686.859
• InChiKey: IKORHOXTEJFGBC-UHFFFAOYSA-M

计算性质

• 辛醇/水分配系数(LogP)：
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• 重原子数：
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• 可旋转键数：
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• 环数：
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• sp3杂化的碳原子比例：
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• 拓扑面积：
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• 氢给体数：
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• 氢受体数：
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反应信息

• 作为产物：
  描述：

  溴甲烷 、 bis(1,2,4-tri-tert-butylcyclopentadienyl)cerium hydride 以 全氘代环己烷 为溶剂， 生成 bis(1,2,4-tri-t-butylcyclopentadienyl)cerium bromide
  参考文献：
  名称：

  Hydrogen for X-Group Exchange in CH₃X (X = Cl, Br, I, OMe, and NMe₂) by Monomeric [1,2,4-(Me₃C)₃C₅H₂]₂CeH: Experimental and Computational Support for a Carbenoid Mechanism

  摘要：

  The reactions between [1,2,4-(Me3C)(3)C5H2](2)CeH, referred to as Cp'2CeH, and CH3X, where X is Cl, Br, I, OMe, and NMe2, are described. The reactions fall into three distinct classes. Class a, where X = Cl, Br, and I, rapidly form Cp'2CeX and CH4 without formation of identifiable intermediates in the H-1 NMR spectra. Class b, where X = Me, proceeds rapidly to CP'Ce-2(eta(2)-CH2OMe) and H-2 and then to CP'2CeOMe and CH4. The methoxymethyl derivative is sufficiently stable to be isolated and characterized, and it is rapidly converted to Cp'2CeOMe in the presence of BPh3. Class c, where X = NMe2, does not result in formation of Cp'2CeNMe2, but deuterium labeling experiments show that H for D exchange occurs in NMe3. Density functional calculations DFT(B3PW91) on the reaction of (C5H5)(2)CeH, referred to as Cp2CeH, and CH3X show that the barrier for alpha-CH activation, resulting in formation of Cp2Ce(eta(2)-CH2X), proceeds with a relatively low activation barrier (Delta G(double dagger)), but the subsequent ejection of CH2 and trapping by H-2 has a higher barrier; the height of the second barrier lies in the order F, Cl, Br, I < OMe << NMe2, consistent with the experimental studies. The DFT calculations also show that the two-step reaction, which proceeds through a carbenoid intermediate, has a lower barrier than a direct one-step or-bond metathesis mechanism. The reaction of Cp2CeCH2OMe and BPh3 is calculated to be a low-activation barrier process, and the ylide, CH2(+)BPh3(-1), is a transition state and not an intermediate.

  DOI：

  10.1021/om9001846

文献信息

• The reaction of bis(1,2,4-tri-t-butylcyclopentadienyl)ceriumbenzyl, Cp′2CeCH2Ph, with methylhalides: a metathesis reaction that does not proceed by a metathesis transition state
  作者：Evan L. Werkema、Richard A. Andersen、Laurent Maron、Odile Eisenstein

  DOI：10.1039/b918103b

  日期：——

  The experimental reaction between [1,2,4-(Me3C)3C5H2]2CeCH2Ph and CH3X, X = F, Cl, Br, and I, yields the metathetical exchange products, [1,2,4-(Me3C)3C5H2]2CeX and CH3CH2Ph. The reaction is complicated by the equilibrium between the benzyl derivative and the metallacycle [1,2,4-(Me3C)3C5H2][(Me3C)2C5H2C(CH3)2CH2]Ce, plus toluene since the metallacycle reacts with CH3X. Labelling studies show that the methyl group of the methylhalide is transferred intact to the benzyl group. The mechanism, as revealed by DFT calculations on (C5H5)2CeCH2Ph and CH3F, does not proceed by way of a four-center mechanism, a σ-bond metathesis, but by a lower barrier process involving a haptotropic shift of the Cp2Ce fragment so that at the transition state the para-carbon of the benzene ring is attached to the Cp2Ce fragment while the CH2 fragment of the benzyl group attacks CH3F that is activated by coordination to the metal ion. As a result the mechanism is classified as an associative interchange process.

  [1,2,4-(Me3C)3C5H2]2Ce Ph 和 X（X = F、Cl、Br 和 I）之间的实验反应产生了元交换产物 [1,2,4-(Me3C)3C5H2]2CeX 和 Ph。苄基衍生物和金属环 [1,2,4-(Me3C)3C5H2][(Me3C)2C5H2C(CH3)2 ]Ce 以及甲苯之间的平衡使反应变得复杂，因为金属环会与 X 发生反应。标记研究表明，甲基卤化物的甲基完整地转移到了苄基上。通过对 (C5H5)2Ce Ph 和 F 的 DFT 计算发现，该机理不是通过四中心机理（Ï-键元合成）进行的，而是通过涉及 Cp2Ce 片段的触变转移的较低障碍过程进行的，因此在过渡态，苯环的对位碳附着在 Cp2Ce 片段上，而苄基的 CH2 片段攻击因与金属离子配位而活化的 F。因此，该机制被归类为关联交换过程。