Mechanistic Investigation into the Gold-Catalyzed Decarboxylative Cross-Coupling of Iodoarenes

While
many gold-catalyzed reactions have been thoroughly developed,
most are not thought to involve redox events at gold. In contrast,
recent advances have demonstrated the feasibility of redox gold catalysis.
This report describes a detailed mechanistic investigation of the
gold-catalyzed decarboxylative cross-coupling, which likely proceeds
via a high-valent Au­(I/III) pathway. This investigation includes a
kinetic analysis, stoichiometric experiments with Au­(III) complexes,
and density functional theory calculations. These data support a turnover-limiting
oxidative addition to form a Au­(III) aryl complex, with an off-cycle
resting state. The dominant pathway appears to proceed through a silver-mediated
decarboxylation with a subsequent Ag­(I) to Au­(III) transmetalation.
These data provide some rationale for the significant counterion effects
between SbF6– and NTf2–.

尽管诸多金催化反应已得到充分开发，但绝大多数被认为不涉及金的氧化还原过程。与之相对，近期研究进展证实了氧化还原金催化的可行性。本报告对金催化脱羧交叉偶联反应开展了详细的机理研究，该反应大概率通过高价Au(I/III)路径进行。本次研究涵盖动力学分析、基于Au(III)配合物的化学计量实验以及密度泛函理论（Density Functional Theory）计算。上述数据支持决速步为氧化加成过程以生成Au(III)芳基配合物，该过程存在循环外休眠态。主导路径似乎通过银介导的脱羧过程进行，随后发生Ag(I)向Au(III)的转金属化反应。上述数据为SbF6–与NTf2–之间存在的显著抗衡离子效应提供了一定的理论依据。