Chemistry Research Laboratory, Department of Chemistry, Oxford University, Oxford, UK OX1 3TA.
Dalton Trans. 2010 Nov 21;39(43):10414-21. doi: 10.1039/c0dt00378f. Epub 2010 Oct 11.
The Pd(II)-catalysed oxidative counterpart of the Heck reaction, originally described by Fujiwara and Moritani, has been studied in detail by a combination of NMR, single-crystal X-ray diffraction and substrate variation. The process involves a palladacycle that is a true intermediate in catalysis. Pd(OAc)(2) is first converted into a more electrophilic palladium species for effective catalysis, defining the main role of added acid. In the course of these studies, three palladacyclic intermediates have been characterised by X-ray diffraction, firstly the directly produced acetate complex 1, the camphorsulfonate complex 2, and additionally tosylate 3, isolated from a reacting system, demonstrating the accessibility of a cationic or comparably electrophilic palladium entity under turnover conditions. The isolated palladacycle 3 is also an effective catalyst. The reaction rate shows a first-order dependency on [anilide] and [Pd], but not on benzoquinone, alkene or p-TsOH. Acid, in the form of p-TsOH, is an essential component, whereas acetate is dispensable. A crossover experiment involving distinct substitution in reactant and palladacycle demonstrates that the palladacycle is directly involved in the catalysis.
Pd(II)催化的 Heck 反应的氧化对应物，最初由 Fujiwara 和 Moritani 描述，通过 NMR、单晶 X 射线衍射和底物变化的组合进行了详细研究。该过程涉及一个钯环，它是催化过程中的真实中间体。Pd(OAc)2 首先转化为更亲电的钯物种，以实现有效的催化，这定义了添加酸的主要作用。在这些研究过程中，通过 X 射线衍射表征了三种钯环中间体，首先是直接生成的乙酸盐配合物 1、樟脑磺酸配合物 2，以及从反应体系中分离出的对甲苯磺酸盐 3，证明了在周转条件下阳离子或类似亲电的钯实体的可及性。分离得到的钯环 3 也是一种有效的催化剂。反应速率对[苯胺]和[Pd]呈一级依赖性，但对苯醌、烯烃或 p-TsOH 没有依赖性。酸（以 p-TsOH 的形式）是必需的组分，而乙酸盐是可有可无的。涉及反应物和钯环中不同取代基的交叉实验表明，钯环直接参与了催化过程。
