A Theoretical DFT-Based and Experimental Study of the Transmetalation Step in Au/Pd-Mediated Cross-Coupling Reactions
A Theoretical DFT-Based and Experimental Study of the Transmetalation Step in Au/Pd-Mediated Cross-Coupling Reactions
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DOI：
10.1002/chem.201301840
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发表时间：
2013-11-04
影响因子：
4.3
通讯作者：
Hashmi, A. Stephen K.
中科院分区：
文献类型：
--
作者：
Hansmann, Max M.;Pernpointner, Markus;Hashmi, A. Stephen K.
在这项工作中，结合理论和实验研究的交叉偶联反应涉及两个金属反应中心，即金和钯，描述。一个金属中心（Au）在此对于其氧化态的变化是相当惰性的，而Pd经历氧化插入和还原消除步骤。详细的机制和精力充沛的研究，每个单独的步骤，重点是关键transmetalation步骤，并比较不同的基板和配体上的催化Pd中心。研究了不同的芳基卤化物（Cl、Br、I）和芳基三氟甲磺酸酯。因此，反阴离子X的性质被证明是至关重要的。在X=Cl和L= PMe 3的情况下，氧化加成是速率决定的，而在X=I的情况下，金属转移步骤在Au/Pd交叉偶联机制中成为速率决定的。各种Au-Pd transmetalation反应方案进行了详细讨论，有利于过渡态与短金属间Au-Pd接触。此外，没有卤化物抗衡阴离子的transmetalation从金（I）到钯（II）是高度吸热的，这证实了我们的实验发现，耦合不发生与芳基三氟甲磺酸酯和类似的弱配位抗衡阴离子的结论是必不可少的，在设计新的Au-Pd催化循环。结合实验工作，这纠正了文献中之前的一份报告，该报告声称在两种金属中与弱配位反阴离子成功偶联可能具有催化作用。
In this work a combined theoretical and experimental investigation of the cross-coupling reaction involving two metallic reaction centers, namely gold and palladium, is described. One metal center (Au) hereby is rather inert towards change in its oxidation state, whereas Pd undergoes oxidative insertion and reductive elimination steps. Detailed mechanistic and energetic studies of each individual step, with the focus on the key transmetalation step are presented and compared for different substrates and ligands on the catalytic Pd center. Different aryl halides (Cl, Br, I) and aryl triflates were investigated. Hereby the nature of the counteranionX turned out to be crucial. In the case of X=Cl and L=PMe3 the oxidative addition is rate-determining, whereas in the case of X=I the transmetalation step becomes rate-determining in the Au/Pd-cross-coupling mechanism. A variety of Au-Pd transmetalation reaction scenarios are discussed in detail, favoring a transition state with short intermetallic Au-Pd contacts. Furthermore, without a halide counteranion the transmetalation from gold(I) to palladium(II) is highly endothermic, which confirms our experimental findings that the coupling does not occur with aryl triflates and similar weakly coordinating counteranionsa conclusion that is essential in designing new Au-Pd catalytic cycles. In combination with experimental work, this corrects a previous report in the literature claiming a successful coupling potentially catalytic in both metals with weakly coordinating counteranions.