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–.

尽管众多金催化反应已得到充分开发，但绝大多数金催化过程均未涉及金中心的氧化还原事件。与之形成鲜明对比的是，近期研究进展证实了氧化还原金催化的可行性。本报道详细阐释了金催化脱羧交叉偶联反应的机理研究，该反应大概率通过高价态Au(I/III)路径进行。本次研究涵盖动力学分析、Au(III)配合物的化学计量实验以及密度泛函理论计算。相关实验数据表明，反应的限速步骤为氧化加成过程，可生成Au(III)芳基配合物，并伴随一个循环外静息态。主导反应路径似乎经由银介导的脱羧过程，随后发生Ag(I)向Au(III)的转金属化步骤。上述数据为六氟锑酸根（SbF6–）与双(三氟甲磺酰)亚胺根（NTf2–）之间存在的显著抗衡离子效应提供了一定的理论依据。