C-H bond activation in dense carbon dioxide: rhodium-catalyzed methane carbonylation and alkane dehydrogenation.
C-H bond activation in dense carbon dioxide: rhodium-catalyzed methane carbonylation and alkane dehydrogenation.
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稠密二氧化碳中的C-H键活化：铑催化的甲烷羰基化和烷烃脱氢。
DOI：
10.1021/jo0102967
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发表时间：
2001
期刊：
影响因子：
--
通讯作者：
T. Sakakura
中科院分区：
文献类型：
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作者：
Jun‐Chul Choi;Yoshinobu Kobayashi;T. Sakakura
在温和条件下烷烃的直接选择性官能化是合成化学家的关键问题之一。 1 分子催化 CrH 键活化的一个主要问题是缺乏合适的溶剂，因为大多数有机溶剂不耐受烷烃活化条件并阻止所需的反应。已经提出了几种化合物来解决这个问题，例如液态氙、2全氟有机物、3和大体积烃。 4 然而，强烈需要更便宜且对催化剂和烷烃具有足够溶解度的反应介质。另一方面，浓密的二氧化碳作为一种高效且环保的反应介质最近引起了越来越多的关注。 5 在本文中，我们报道了在浓密二氧化碳中通过分子催化进行的甲烷羰基化和烷烃脱氢。尽管最近尝试了超临界二氧化碳中钌催化的烷烃转化，但没有观察到 CrH 键活化。 6 从所谓的“绿色化学”角度来看，基于甲烷的基础化学品的生产非常重要，因为甲烷是一种典型的可持续资源。 7 我们一直在研究RhCl (L)(PMe3) 2rhv 体系(L) 两个电子给体配体催化的烷烃直接羰基化和脱氢反应。 8 在这些反应中，烷烃本身用作反应介质来溶解底物和催化剂。然而，由于甲烷的沸点较低，该方法很难应用于甲烷转化。在这种情况下，浓密的二氧化碳作为反应介质似乎非常有前途，因为它可与甲烷等气态化合物混溶，并且可能足够稳定，可以在烷烃活化条件下生存。因此，我们研究了二氧化碳中甲烷的羰基化（eq 1）。典型的实验如下进行。在4℃下，将带有蓝宝石窗的高压釜（20cm3内容积）填充铑络合物（0.014mmol）、一氧化碳（3atm）、甲烷（110atm）和二氧化碳（总压高达300atm）。然后用250W高压汞灯（USHIO SP3-250）将反应混合物照射16小时。使用毛细管柱通过 GC 对反应产物进行分析，所有挥发性产物也通过 GCrMS 进行表征。
The direct and selective functionalization of alkanes under mild conditions is one of the key issues for synthetic chemists. 1 A major problem in CrH bond activation by molecular catalysis is the lack of suitable solvents because most organic solvents are not tolerant under alkane activation conditions and prevent the desired reactions. Several compounds have been proposed for solving this problem, such as liquid xenon, 2 perfluoro organics, 3 and bulky hydrocarbons. 4 However, more inexpensive reaction media with adequate solubility for both the catalysts and alkanes are strongly desired. On the other hand, dense carbon dioxide has recently attracted increasing attention as an efficient and environmentally friendly reaction medium. 5 In the present paper, we report the methane carbonylation and alkane dehydrogenation by molecular catalysis in dense carbon dioxide. Although ruthenium-catalyzed alkane conversion in supercritical carbon dioxide was attempted recently, no CrH bond activation was observed. 6 The production of fundamental chemicals based on methane is of great importance in view of so-called “green chemistry” because methane is a typical sustainable resource. 7 We have been investigating the direct carbonylation and dehydrogenation of alkanes catalyzed by the RhCl (L)(PMe3) 2rhv system (L) two electron-donor ligands). 8 In these reactions, the alkane itself was used as a reaction medium to dissolve the substrates and the catalyst. However, this methodology is hard to apply to methane transformation due to the low boiling point of methane. In this context, dense carbon dioxide seems very promising as a reaction medium because it is miscible with gaseous compounds such as methane and possibly stable enough to survive under alkane activation conditions. Hence, we examined the carbonylation of methane in carbon dioxide (eq 1).A typical experiment was carried out as follows. An autoclave with sapphire windows (20 cm3 inner volume) was filled with a rhodium complex (0.014 mmol), carbon monoxide (3 atm), methane (110 atm), and carbon dioxide (up to 300 atm total pressure) at 4 C. The reaction mixture was then irradiated for 16 h with a 250 W highpressure mercury lamp (USHIO SP3-250). The reaction products were analyzed by GC using a capillary column, and all the volatile products were also characterized by GCrMS.