Ru-Catalyzed C-H Arylation of Fluoroarenes with Aryl Halides

Simonetti, Marco, Perry, Gregory J.P., Cambeiro, Xacobe C., Juliá-Hernández, Francisco, Arokianathar, Jude N. and Larrosa, Igor (2016) Ru-Catalyzed C-H Arylation of Fluoroarenes with Aryl Halides. Journal of the American Chemical Society, 138 (10), 3596-3606. (doi:10.1021/jacs.6b01615).

Abstract

Although the ruthenium-catalyzed C-H arylation of arenes bearing directing groups with haloarenes is well-known, this process has never been achieved in the absence of directing groups. We report the first example of such a process and show that unexpectedly the reaction only takes place in the presence of catalytic amounts of a benzoic acid. Furthermore, contrary to other transition metals, the arylation site selectivity is governed by both electronic and steric factors. Stoichiometric and NMR mechanistic studies support a catalytic cycle that involves a well-defined Η⁶-arene-ligand-free Ru(II) catalyst. Indeed, upon initial pivalate-assisted C-H activation, the aryl-Ru(II) intermediate generated is able to react with an aryl bromide coupling partner only in the presence of a benzoate additive. In contrast, directing-group-containing substrates (such as 2-phenylpyridine) do not require a benzoate additive. Deuterium labeling and kinetic isotope effect experiments indicate that C-H activation is both reversible and kinetically significant. Computational studies support a concerted metalation-deprotonation (CMD)-type ruthenation mode and shed light on the unusual arylation regioselectivity.

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Contributors

Author: Gregory J.P. Perry

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