Multi-technique Approach to Reveal the Mechanism of Cu(II) Catalyzed Arylation Reactions
Multi-technique Approach to Reveal the Mechanism of Cu(II) Catalyzed Arylation Reactions
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多技术方法揭示 Cu(II) 催化芳基化反应的机理
DOI：
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发表时间：
2004
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通讯作者：
A. M. Yatim
中科院分区：
文献类型：
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作者：
A. M. Yatim
介绍了多种原位和时间分辨光谱技术(EDXAFS、UV-Vis、EPR、核磁共振、X射线衍射谱)，揭示了重要的厌氧铜(II)催化的咪唑N-芳基化反应中间体的详细结构和电子信息。在此基础上，提出了铜(II)催化芳基化反应的新机理。在常温常压下，在NMP/H2O混合溶剂中，用市售铜催化剂[Cu(OH)(TMEDA)]2Cl2(I)催化咪唑的N-芳基化反应。结果表明，该体系是一种良好、有效的催化剂。该反应不需要氧气或碱的存在。然而，水的存在是反应继续进行所必需的。光谱研究结果对几种反应中间体进行了表征。反应的第一步和选择性决定步骤是二聚体铜(II)络合物与咪唑的反应，生成单体铜(II)(咪唑)中间体II。随后与苯基硼酸反应生成铜(III)(咪唑)(苯基)中间体III，该中间体经过还原消除后形成苯基咪唑产物和铜(I)单体物种IV。最后，铜物种被重新氧化，形成回来的铜(II)单体和二聚体配合物。观察到咪唑和苯并咪唑的抑制作用。苯基硼酸与水结合，参与了所述催化循环中的氧化和再氧化步骤。
Multiple in situ and time-resolved spectroscopic techniques (EDXAFS, UV-Vis, EPR, NMR, XRD) are described to reveal detailed structural and electronic information on reaction intermediates of an important, anaerobic Cu(II) catalyzed N-arylation of imidazole. Based on these results, a novel mechanism for this Cu(II) catalyzed arylation reaction is proposed. The N-arylation of imidazole was performed in a NMP/H2O solvent mixture, at ambient temperature and atmosphere, using the commercially available Cu-catalyst [Cu(OH)(TMEDA)]2Cl2 (I). The system was shown to be a good and effective catalyst. The reaction does not require the presence of dioxygen or a base. The presence of H2O is however necessary for the reaction to proceed. The spectroscopic study resulted in the characterization of several reaction intermediates. The first and selectivity determining step in the reaction is the reaction of the dimeric Cu(II) complex with imidazole, forming a monomeric Cu(II)(Imidazole) intermediate II. Upon subsequent addition of phenylboronic acid an Cu(III)(imidazolate)(phenyl) intermediate III is formed, which after reductive elimination forms the phenylimidazole product and the Cu(I) monomeric species IV as characterized here. Finally, the Cu species is reoxidized forming back Cu(II) monomeric and dimer complexes. Inhibition by imidazole and phenylimidazole is observed. The phenylboronic acid is, in combination with H2O, involved in the oxidation and reoxidation steps in the described catalytic cycle.