Mechanism of Cu/Pd-catalyzed decarboxylative cross-couplings: a DFT investigation.
Mechanism of Cu/Pd-catalyzed decarboxylative cross-couplings: a DFT investigation.
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DOI：
10.1021/ja503295x
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发表时间：
2014-07
影响因子：
15
通讯作者：
Andreas Fromm;Christoph van Wüllen;D. Hackenberger;L. Goossen
中科院分区：
文献类型：
--
作者：
Andreas Fromm;Christoph van Wüllen;D. Hackenberger;L. Goossen
用密度泛函方法研究了在铜/钯体系协同催化下，苯甲酸酯与卤代芳烃脱羧基交叉偶联生成联芳基的反应机理。计算了2-和4-氟苯甲酸钾与溴苯在铜(I)/1，10-邻菲咯啉和阴离子单膦钯配合物[Pd(PMe3)Br](-)催化体系中的两个模型反应的起始原料、产物、中间体和过渡态的几何构型和能量。比较了几种中性途径和阴离子途径，确定了合理的催化循环。关键的发现是，转金属作用与脱羧基具有相当高的屏障，而脱羧基以前被认为是唯一的速率决定因素。转金属反应的电子活化能比较合理，但初始形成铜/钯加合物时的自由能损失较大。这些结果表明，旨在进一步改进催化剂的研究应该针对可能有助于形成双金属中间体的桥联双齿配体。实验研究证实了这一有点违反直觉的预测。有了双齿、潜在的桥联配体，旨在支持双金属加合物的形成，脱酸偶联的反应温度降低了70℃，仅为100℃。
The reaction mechanism of decarboxylative cross-couplings of benzoates with aryl halides to give biaryls, which is cooperatively catalyzed by copper/palladium systems, was investigated with DFT methods. The geometries and energies of all starting materials, products, intermediates, and transition states of the catalytic cycle were calculated for the two model reactions of potassium 2- and 4-fluorobenzoate with bromobenzene in the presence of a catalyst system consisting of copper(I)/1,10-phenanthroline and the anionic monophosphine palladium complex [Pd(PMe3)Br](-). Several neutral and anionic pathways were compared, and a reasonable catalytic cycle was identified. The key finding is that the transmetalation has a comparably high barrier as the decarboxylation, which was previously believed to be solely rate-determining. The electronic activation energy of the transmetalation is rather reasonable, but the free energy loss in the initial Cu/Pd adduct formation is high. These results suggested that research aimed at further improving the catalyst should target potentially bridging bidentate ligands likely to assist in the formation of bimetallic intermediates. Experimental studies confirm this somewhat counterintuitive prediction. With a bidentate, potentially bridging ligand, designed to support the formation of bimetallic adducts, the reaction temperature for decarboxylative couplings was reduced by 70 °C to only 100 °C.