Palladium-Catalyzed Aerobic Homocoupling of Alkynes: Full Mechanistic Characterization of a More Complex Oxidase-Type Behavior,ACS Catalysis

当前位置： X-MOL 学术 › ACS Catal. › 论文详情

Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)

Palladium-Catalyzed Aerobic Homocoupling of Alkynes: Full Mechanistic Characterization of a More Complex Oxidase-Type Behavior
ACS Catalysis ( IF 11.3 ) Pub Date : 2018-07-05 00:00:00 , DOI: 10.1021/acscatal.8b01540
Alberto Toledo ₁ , Ignacio Funes-Ardoiz ₂ , Feliu Maseras _{2,

3} , Ana C. Albéniz ₁

Affiliation

A combined experimental and computational approach has been used to shed light on the mechanism of the Pd-catalyzed oxidative homocoupling of alkynes using oxygen as the oxidant. Mechanistic understanding is important because of the synthetically relevant direct involvement of oxygen in the oxidative coupling and because of the presence of related processes as undesired side reactions in cross-coupling reactions involving terminal alkynes. A low-ligated [Pd(PPh₃)(alkyne)] complex is key in the process, and it can be conveniently generated from allylic palladium(II) complexes in the presence of a base or from Pd(I) allylic dimers as precatalysts. The catalytic coupling occurs by alkyne metalation to give an anionic [Pd(PPh₃)(alkynyl)]⁻ complex that is then oxidized by oxygen. The interaction with oxygen occurs only on this electron-rich Pd(0) anionic species and leads to a (κO,κO-peroxo)palladium(II) singlet intermediate that undergoes subsequent protonolysis to give a (κO-hydroperoxo)palladium(II) complex and then hydrogen peroxide. The second alkyne metalation occurs on a Pd(II) derivative to give a bis(alkynyl)palladium(II) complex that evolves to the product by reductive elimination as the product-forming step. This reaction is an oxidase-type process that, in contrast to most Pd-catalyzed oxidative processes, occurs without separation of the substrate transformation and the catalyst oxidation, with these two processes being intertwined and dependent on one another.

中文翻译：

钯催化的炔烃有氧同质偶联：更复杂的氧化酶类型行为的完整机制表征。

实验和计算相结合的方法已被用来阐明氧作为氧化剂的炔烃在钯催化的氧化均偶联反应中的作用机理。机理上的理解是重要的，这是因为氧在氧化偶联中具有合成相关的直接参与，并且由于涉及末端炔烃的交叉偶联反应中存在作为不希望的副反应的相关过程。低连接的[Pd（PPh ₃）（炔烃）]络合物是该过程的关键，它可以在碱存在下从烯丙基钯（II）络合物方便地生成，也可以从Pd（I）烯丙基二聚体作为预催化剂生成。。催化偶联通过炔烃金属化作用而产生，以产生阴离子型[Pd（PPh ₃）（炔基）] ^-然后被氧气氧化的复合物。与氧的相互作用仅在此富电子的Pd（0）阴离子物质和通向发生时（κ ø，κ ö μ-过氧）钯（II）的单重中间经历随后的质子分解，得到（κ ö -hydroperoxo）钯（二）络合物再过氧化氢。第二次炔属金属化反应发生在Pd（II）衍生物上，生成双（炔基）钯（II）配合物，该配合物通过还原消除作为产物形成步骤而演变为产物。该反应是一种氧化酶类型的过程，与大多数Pd催化的氧化过程相反，该过程在没有分离底物转化和催化剂氧化的情况下发生，这两个过程相互缠绕并相互依赖。

更新日期：2018-07-05

点击分享查看原文

点击收藏

公开下载

阅读更多本刊最新论文本刊介绍/投稿指南11