Max-Planck-Institut für Kohlenforschung, 45470 Mülheim/Ruhr, Germany.
J Am Chem Soc. 2020 Oct 28;142(43):18541-18553. doi: 10.1021/jacs.0c07808. Epub 2020 Oct 19.
The only recently discovered -hydrogenation of internal alkynes is a fundamentally new transformation, in which both H atoms of dihydrogen are transferred to the same C atom of a triple bond while the other position transforms into a discrete metal carbene complex. [Cp*RuCl] is presently the catalyst of choice: the resulting piano-stool ruthenium carbenes can engage a tethered alkene into either cyclopropanation or metathesis, and a prototypical example of such a reactive intermediate with an olefin ligated to the ruthenium center has been isolated and characterized by X-ray diffraction. It is the substitution pattern of the olefin that determines whether metathesis or cyclopropanation takes place: a systematic survey using alkenes of largely different character in combination with a computational study of the mechanism at the local coupled cluster level of theory allowed the preparative results to be sorted and an intuitive model with predictive power to be proposed. This model links the course of the reaction to the polarization of the double bond as well as to the stability of the secondary carbene complex formed, if metathesis were to take place. The first application of "hydrogenative metathesis" to the total synthesis of sinularones E and F concurred with this interpretation and allowed the proposed structure of these marine natural products to be confirmed. During this synthesis, it was found that -hydrogenation also provides opportunities for C-H functionalization. Moreover, silylated alkynes are shown to participate well in hydrogenative metathesis, which opens a new entry into valuable allylsilane building blocks. Crystallographic evidence suggests that the polarized [Ru-Cl] bond of the catalyst interacts with the neighboring RSi group. Since attractive interligand Cl/RSi contacts had already previously been invoked to explain the outcome of various ruthenium-catalyzed reactions, including -hydrosilylation, the experimental confirmation provided herein has implications beyond the present case.
内部炔烃的氢化作用是最近才发现的，它是一种全新的转化，其中氢气的两个 H 原子同时转移到三键的同一个 C 原子上，而另一个位置则转化为离散的金属卡宾络合物。[Cp*RuCl] 是目前的首选催化剂：生成的钢琴凳型钌卡宾可以使连接的烯烃发生环丙烷化或交叉复分解反应，并且与连接到钌中心的烯烃配位的这种反应性中间体的典型例子已通过 X 射线衍射分离并表征。烯烃的取代模式决定了发生交叉复分解反应还是环丙烷化反应：使用性质差异很大的烯烃进行系统调查，并在局部耦合簇理论水平上对机理进行计算研究，使制备结果得以分类，并提出了具有预测能力的直观模型。该模型将反应过程与双键的极化以及如果发生交叉复分解反应则形成的次级卡宾络合物的稳定性联系起来。“加氢交叉复分解反应”在 sinularones E 和 F 的全合成中的首次应用与该解释一致，并允许确认这些海洋天然产物的提出的结构。在该合成过程中，发现 -氢化还为 C-H 官能化提供了机会。此外，硅化的炔烃也很好地参与了加氢交叉复分解反应，这为有价值的烯丙基硅烷砌块开辟了新途径。晶体学证据表明，催化剂的极化 [Ru-Cl] 键与相邻的 RSi 基团相互作用。由于先前已经引入了有吸引力的配体 Cl/RSi 接触来解释各种钌催化反应的结果，包括 -硅氢化反应，因此本文提供的实验证实具有超出当前情况的意义。
