Browsing by Subject "Catalysts"

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    Ru-catalyzed C–H arylation of fluoroarenes with aryl halides
    (American Chemical Society, 2016-03-04) Simonetti, Marco; Perry, Gregory J. P.; Cambeiro, Xacobe C.; Juliá Hernández, Francisco; Arokianathar, Jude N.; Larrosa, Igor; Química Inorgánica
    Although the ruthenium-catalyzed C−H arylation of arenes bearing directing groups with haloarenes is wellknown, 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-ligandfree 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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    Walking metals for remote functionalization
    (American Chemical Society, 2018-02-08) Sommer, Heiko; Juliá Hernández, Francisco; Martin, Ruben; Marek, Ilan; Química Inorgánica
    The distant and selective activation of unreactive C−H and C−C bonds remains one of the biggest challenges in organic chemistry. In recent years, the development of remote functionalization has received growing interest as it allows for the activation of rather challenging C−H and C−C bonds distant from the initiation point by means of a “metal-walk”. A “metal-walk” or “chain-walk” is defined by an iterative series of consecutive 1,2- or 1,3-hydride shifts of a metal complex along a single hydrocarbon chain. With this approach, simple building blocks or mixtures thereof can be transformed into complex scaffolds in a convergent and unified strategy. A variety of catalytic systems have been developed and refined over the past decade ranging from late-transition-metal complexes to more sustainable iron- and cobalt-based systems. As the possibilities of this field are slowly unfolding, this area of research will contribute considerably to provide solutions to yet unmet synthetic challenges.