ABSTRACT:The intramolecular gold-catalyzed arylation of arenes by aryltrimethylsilanes has been investigated from both a mechanistic and preparative aspect. The reaction generates five to nine membered rings, and of the 44 examples studied, ten include a heteroatom (N, O). The tethering of the arene to the arylsilane not only provides 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 electronics of the arene and changes from reductive elimination to π-complexation for arenes bearing strongly electronwithdrawing substituents (σ >0.43). Reductive elimination is accelerated by electron-donating substituents ( = ̶ 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 results in faster reductive elimination from Ar-Au(X)-Ar, and to the π-complexation of the arene by Ar-AuX2 becoming the turnover-limiting step.

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Domino catalysis is a well-explored route to increasing the efficiency of multistep reactions. However, the kinetic features required for efficient turnover of a process where "multiple transformations are effected by a single catalytic mechanism" have not been explored in any detail. The kinetics of a nominally simple two-stage domino catalytic reaction have been analyzed by way of a gold-catalyzed coupling of two electron-deficient arylsilanes to generate an arylated fluorene. A combination of in situ interleaved 1 H and 19 F NMR spectroscopic kinetic measurements, kinetic simulations, and variations in substitution reveal how the catalyst partitioning between the two different cycles impacts both the rate and the selectivity of the process. The insight enables identification that sequential catalyst speciation and accumulation of the domino intermediate are general kinetic criteria for efficient domino catalysis.

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