Probing the reactivity of a stable silene using muonium.
Probing the reactivity of a stable silene using muonium.
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DOI：
10.1002/anie.200804458
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发表时间：
2008-12
影响因子：
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通讯作者：
Brett M. McCollum;T. Abe;J. Brodovitch;Jason A. C. Clyburne;T. Iwamoto;M. Kira;P. W. Percival;R. West
中科院分区：
文献类型：
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作者：
Brett M. McCollum;T. Abe;J. Brodovitch;Jason A. C. Clyburne;T. Iwamoto;M. Kira;P. W. Percival;R. West
自1981年发现稳定的多键硅化合物以来，硅烯（R2 Si = CR2）的合成和反应性一直是研究的主要焦点，并且已经发表了许多关于这一问题的评论文章。[1]然而，尽管在这一领域的活动水平，有很少的了解硅烯的自由基化学。亚甲硅烷基2，2，5，5-四（三甲基甲硅烷基）硅杂环戊烷-1，1-二基1在室温下通过三甲基甲硅烷基的1，2-迁移重排为亚甲硅烷基1，2，5，5-四（三甲基甲硅烷基）硅杂环戊烯2（方案1）. [2]在这里，我们报告使用的类似物的氢原子作为探针的相对反应性的silenic碳和硅原子的2朝向自由基加成。氢原子是一个特殊的探针的反应性，因为它的小尺寸最大限度地减少空间位阻和其简单的结构避免了额外的电子效应，我们认为氢原子是一个公正的自由基探针，因为它是单原子，因此，不极性。然而，氢原子并不是溶液研究的常用试剂，主要是因为其生成过程中固有的复杂性。氢原子通常通过水或其他质子溶剂的光解或辐解产生，不可避免地产生额外的自由基物质。我们没有使用H原子来产生自由基和电子自旋共振来检测它们，而是使用了μ素（Mu=[μ+ eR]），并通过统称为μ子自旋旋转和共振（μSR）的技术来检测自由基。[3-6]μ 鎓是一种单电子原子，其原子核是正μ子。它在化学上与H等价，但质量只有H的九分之一。μ素作为氢原子化学的探针的效用是有据可查的。[7-9]在支持资料中给出了在这项工作中使用的μSR技术的简要描述。2在四氢呋喃中的1.5 m溶液被放置在正μ子束中，并通过横向场μ子自旋旋转谱（TF-μSR）进行了研究。当正μ子停止在物质中时，一部分（在典型的有机化合物中占30-40%）结合电子并形成μ 鎓，然后可以与不饱和分子反应，就像H一样。在298 K下在14.5 kG磁场中收集的TF-μSR光谱如图1所示。在高磁场下，
Since the discovery of stable multiply bonded silicon compounds in 1981, the synthesis and reactivity of silenes (R2Si= CR2) has been a major focus of research and many review articles have been published on this matter.[1] However, despite the level of activity in this field, there is little understanding of the radical chemistry of silenes. The silylene 2, 2, 5, 5-tetrakis (trimethylsilyl) silacyclopentane-1, 1-diyl, 1, rearranges to the silene 1, 2, 5, 5-tetrakis (trimethylsilyl) silacyclopentene, 2, at room temperature by 1, 2-migration of a trimethylsilyl group (Scheme 1).[2] Herein, we report the use of an analogue of the hydrogen atom as a probe of the relative reactivity of the silenic carbon and silicon atoms of 2 toward radical addition. The hydrogen atom is an exceptional probe of reactivity because its small size minimizes steric obstruction and its simple structure avoids additional electronic effects; we consider the hydrogen atom to be an unbiased radical probe, since it is monoatomic and, therefore, not polar. However, the hydrogen atom is not a common reagent for solution studies, largely because of complications inherent in its generation. Hydrogen atoms are usually produced by photolysis or radiolysis of water or other protic solvents, inevitably resulting in additional radical species. Rather than make use of H atoms to generate radicals and electron spin resonance to detect them, we have employed muonium (Mu=[μ+ eÀ]), and detected radicals by techniques collectively known as muon spin rotation and resonance (μSR).[3–6] Muonium is a single-electron atom whose nucleus is the positive muon. It is chemically equivalent to H, but has only one-ninth the mass. The utility of muonium as a probe of hydrogen atom chemistry is well documented.[7–9] A brief description of the μSR techniques used in this work is given in the Supporting Information.A 1.5 m solution of 2 in tetrahydrofuran was placed in a beam of positive muons and investigated by transverse-field muon spin rotation spectroscopy (TF-μSR). When positive muons stop in matter, a fraction (30–40% in typical organic compounds) bind electrons and form muonium, which can then react with unsaturated molecules, as H does. The TF-μSR spectrum collected at 298K in a magnetic field of 14.5 kG is shown in Figure1. At high magnetic fields,