Exceptionally low-temperature carbon-hydrogen/carbon-deuterium exchange reactions of organic and organometallic compounds catalyzed by the Cp*(PMe3)IrH(ClCH2Cl)+ cation
Exceptionally low-temperature carbon-hydrogen/carbon-deuterium exchange reactions of organic and organometallic compounds catalyzed by the Cp*(PMe3)IrH(ClCH2Cl)+ cation
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DOI：
10.1021/ja0155480
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发表时间：
2001-06-20
影响因子：
15
通讯作者：
Bergman, RG
中科院分区：
文献类型：
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作者：
Golden, JT;Andersen, RA;Bergman, RG
由于金属介导的碳氢键活化可以在饱和碳氢化合物转化为更有用的功能化有机化合物的过程中发挥作用，人们已经努力开发在溶液中进行这种转化的温和方法。激活CH键的大多数经典方法涉及与不带电、富电子、配位不饱和金属中心的氧化加成反应（eq 1）。然而，最近发现了几个发生在阳离子“亲电性”晚期过渡金属中心的新的CH活化反应，重新引起了人们对这类CH活化反应的兴趣（eq 2）。2-8这类反应中的大多数需要升高温度。前体几乎总是金属烷基或芳基；很少有晚期金属氢化物被证明能促进这些反应。在本文中，我们报告了(a)一种长期寻找的简单单体阳离子氢化铱的合成，(b)证明这种材料以意想不到的高速率和意想不到的低温诱导烷烃CH活化，以及(c)这种模式的CH活化可能涉及一种二氢烷基中间体，该中间体只经历烷烃而不是H2的还原消除。阳离子体系[Cp*(PMe3) IrMe (ClCH2Cl)]+[B (3,5 - c6h3 -(CF3) 2) 4]-， 3以其激活CH键的能力而闻名。例如，[Cp*(PMe3) IrMe (ClCH2Cl)]+[MeB (C6F5) 3]-(1)与同位素标记的甲烷在10℃下反应，将铱结合的甲基交换为标记的甲基。我们一直对合成[Cp*(PMe3) IrH-(ClCH2Cl)]+ X-(2)等配合物感兴趣，并将它们与类似的甲基锂离子离子进行比较。设计提供这种材料的方法以未知的机制导致三氢化物[Cp*(PMe3) IrH3]+(3) 9和/或[Cp*(PMe3)-HIr-H-IrH (PMe3) Cp*]+(4)， 10的盐。我们找到了解决这个棘手问题的方法，同时开发了一种新的方法来生成甲基阳离子1，利用氟芳基硼烷从电荷中性金属中心提取甲基的能力。因此，在CD2Cl2 at-84 C中，将三氟苯硼烷12加成到Cp*(PMe3) IrMe2 13上，可定量生成甲基阳离子1。14少量过量硼烷（1.2当量）用于确保完全转化为所需的阳离子甲基锂络合物。
Because of the role that metal-mediated carbon-hydrogen bond activation could play in the conversion of saturated hydrocarbons to more useful, functionalized organic compounds, much effort has gone into developing mild methods for carrying out this transformation in solution. 1 Most of the classical methods for activating CH bonds involve oxidative addition reactions with uncharged, electron-rich, coordinatively unsaturated metal centers (eq 1). Recently, however, several new CH activation reactions have been discovered that take place at cationic “electrophilic” late transition metal centers, creating a resurgence of interest in this class of CH activating reactions (eq 2). 2-8 Most of the reactions in this class require elevated temperatures. The precursors are nearly always metal alkyls or aryls: few late metal hydrides have been shown to promote these reactions. Herein, we report (a) the synthesis of a long-sought simple, monomeric cationic iridium hydride,(b) the demonstration that this material induces alkane CH activation at an unexpectedly high rate and surprisingly low temperature, and (c) that this mode of CH activation likely involves a dihydridoalkyl intermediate that undergoes reductive elimination of only alkane and not H2. The cation system,[Cp*(PMe3) IrMe (ClCH2Cl)]+[B (3, 5-C6H3-(CF3) 2) 4]-, 3 is known for its ability to activate CH bonds. For example,[Cp*(PMe3) IrMe (ClCH2Cl)]+[MeB (C6F5) 3]-(1) reacts with isotopically labeled methane at-10 C to exchange the iridium-bound methyl group for a labeled one. We have been interested in synthesizing complexes such as [Cp*(PMe3) IrH-(ClCH2Cl)]+ X-(2) to compare them to the analogous methyliridium cation. Methods designed to provide this material led to salts of the trihydrides [Cp*(PMe3) IrH3]+(3) 9 and/or [Cp*(PMe3)-HIr-H-IrH (PMe3) Cp*]+(4), 10 by unknown mechanisms.We found a solution to this vexing problem while developing a new method for generating methyl cation 1 that utilizes the ability of fluoroarylboranes to abstract a methyl group from charge-neutral metal centers. 11 Thus, addition of trispentafluorophenylborane12 to Cp*(PMe3) IrMe2 13 in CD2Cl2 at-84 C results in the quantitative formation of methyl cation 1. 14 A slight excess of borane (1.2 equiv) is used to ensure complete conversion to the desired cationic methyliridium complex.