EaStChem, University of Edinburgh , Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, U.K.
School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, U.K.
J Am Chem Soc. 2017 Jan 11;139(1):245-254. doi: 10.1021/jacs.6b10018. Epub 2016 Dec 29.
The intramolecular gold-catalyzed arylation of arenes by aryl-trimethylsilanes has been investigated from both mechanistic and preparative aspects. The reaction generates 5- to 9-membered rings, and of the 44 examples studied, 10 include a heteroatom (N, O). Tethering of the arene to the arylsilane provides not only a tool to probe the impact of the conformational flexibility of Ar-Au-Ar intermediates, via systematic modulation of the length of aryl-aryl linkage, but also the ability to arylate neutral and electron-poor arenes-substrates that do not react at all in the intermolecular process. Rendering the arylation intramolecular also results in phenomenologically simpler reaction kinetics, and overall these features have facilitated a detailed study of linear free energy relationships, kinetic isotope effects, and the first quantitative experimental data on the effects of aryl electron demand and conformational freedom on the rate of reductive elimination from diaryl-gold(III) species. The turnover-limiting step for the formation of a series of fluorene derivatives is sensitive to the reactivity of the arene and changes from reductive elimination to π-complexation for arenes bearing strongly electron-withdrawing substituents (σ > 0.43). Reductive elimination is accelerated by electron-donating substituents (ρ = -2.0) on one or both rings, with the individual σ-values being additive in nature. Longer and more flexible tethers between the two aryl rings result in faster reductive elimination from Ar-Au(X)-Ar and lead to the π-complexation of the arene by Ar-AuX becoming the turnover-limiting step.
芳基三甲基硅烷与芳烃的分子内金催化芳基化反应已从机理和制备两个方面进行了研究。该反应生成 5 到 9 元环，在所研究的 44 个例子中，有 10 个包含杂原子（N，O）。芳烃与芳基硅烷的连接不仅提供了一种工具，可以通过系统地调节芳基-芳基键的长度来探测 Ar-Au-Ar 中间体构象灵活性的影响，而且还可以对中性和缺电子芳烃进行芳基化-底物在分子间过程中根本不反应。使芳基化成为分子内也导致了更简单的反应动力学现象，总的来说，这些特征促进了线性自由能关系、动力学同位素效应以及关于芳基电子需求和构象自由度对二芳基金（III）物种还原消除速率的影响的第一批定量实验数据的详细研究。一系列芴衍生物的形成的周转率限制步骤对芳烃的反应性敏感，并从还原消除变为对带有强吸电子取代基的芳烃的π-络合（σ>0.43）。供电子取代基（ρ=-2.0）在一个或两个环上加速还原消除，单独的σ值在性质上是加性的。两个芳基环之间更长且更灵活的键导致 Ar-Au（X）-Ar 中的还原消除更快，并导致芳基通过 Ar-AuX 发生π-络合成为周转率限制步骤。
