Kubota Koji, Kawamura Sota, Jiang Julong, Maeda Satoshi, Ito Hajime
Division of Applied Chemistry and Frontier Chemistry Center, Faculty of Engineering, Hokkaido University Sapporo Hokkaido Japan
Institute for Chemical Reaction Design and Discovery (WPI-ICReDD), Hokkaido University Sapporo Hokkaido Japan.
Chem Sci. 2024 Oct 1;15(42):17453-9. doi: 10.1039/d4sc05361c.
Organobarium reagents are of interest as homologues of the Grignard reagents based on organomagnesium compounds due to their unique reactivity as well as regio- and stereoselectivity. However, reactions involving organobarium reagents are less developed in comparison to reactions involving Grignard reagents due to the lack of a simple and economical synthetic method and their high reactivity. To the best of our knowledge, there is no established method for the direct synthesis of organobarium compounds from commercially available bulk barium metal and organic halides. So far, the generation of organobarium compounds usually requires the use of activated barium (Rieke barium), which significantly reduces the practical utility of organobarium reagents and hinders the development of new organobarium-mediated transformations. Here, we present a mechanochemical strategy based on ball-milling that facilitates the direct generation of various aryl barium nucleophiles from commercially available unactivated barium metal and aryl halides without complicated pre-activation processes. Our simple mechanochemical protocol allows the rapid development of novel carbon-silicon-bond-forming reactions with hydrosilanes mediated by aryl barium nucleophiles; importantly, these reactions are difficult to achieve using other Grignard-type carbon nucleophiles. To the best of our knowledge, this is the first example of a nucleophilic substitution reaction involving an aryl barium species. Furthermore, this mechanochemical strategy established the first example of a nucleophilic addition to a carbonyl compound involving an aryl barium nucleophile. Preliminary theoretical calculations using the artificial force-induced reaction (AFIR) method to reveal the reaction mechanism of the hydrosilane arylation are also described.
有机钡试剂作为基于有机镁化合物的格氏试剂的同系物而备受关注，这是由于它们具有独特的反应活性以及区域和立体选择性。然而，与涉及格氏试剂的反应相比，涉及有机钡试剂的反应发展较少，这是因为缺乏简单且经济的合成方法以及它们的高反应活性。据我们所知，目前还没有从市售的块状钡金属和有机卤化物直接合成有机钡化合物的成熟方法。到目前为止，有机钡化合物的生成通常需要使用活性钡（Rieke钡），这显著降低了有机钡试剂的实际应用价值，并阻碍了新的有机钡介导的转化反应的发展。在此，我们提出一种基于球磨的机械化学策略，该策略无需复杂的预活化过程，就能从市售的未活化钡金属和芳基卤化物直接生成各种芳基钡亲核试剂。我们简单的机械化学方案能够快速开发由芳基钡亲核试剂介导的与硅烷的新型碳 - 硅键形成反应；重要的是，使用其他格氏型碳亲核试剂很难实现这些反应。据我们所知，这是涉及芳基钡物种的亲核取代反应的首个实例。此外，这种机械化学策略建立了涉及芳基钡亲核试剂的羰基化合物亲核加成反应的首个实例。还描述了使用人工力诱导反应（AFIR）方法进行的初步理论计算，以揭示硅烷芳基化反应的机理。
