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Arylation of hydrocarbons enabled by organosilicon reagents and weakly coordinating anions

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Science  31 Mar 2017:
Vol. 355, Issue 6332, pp. 1403-1407
DOI: 10.1126/science.aam7975

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Turning benzene into a C–H bond cleaver

Ask chemists for the best way to break a strong bond, and they will tell you to make an even stronger one. Shao et al. applied this principle by using silicon-fluorine bonds to break carbon-hydrogen bonds. They prepared benzene rings with adjacent fluorine and silicon substituents. Then they used a little extra activated silicon, paired with a carborane, to prime a cycle that draws away the fluorine to produce a cation-like aryl intermediate. This intermediate can then slice through the typically inert C–H bonds in alkanes, including methane. The alkylated rings go on to release their silicon, which keeps the process going.

Science, this issue p. 1403

Abstract

Over the past 80 years, phenyl cation intermediates have been implicated in a variety of C–H arylation reactions. Although these examples have inspired several theoretical and mechanistic studies, aryl cation equivalents have received limited attention in organic methodology. Their high-energy, promiscuous reactivity profiles have hampered applications in selective intermolecular processes. We report a reaction design that overcomes these challenges. Specifically, we found that β-silicon–stabilized aryl cation equivalents, generated via silylium-mediated fluoride activation, undergo insertion into sp3 and sp2 C–H bonds. This reaction manifold provides a framework for the catalytic arylation of hydrocarbons, including simple alkanes such as methane. This process uses low loadings of Earth-abundant initiators (1 to 5 mole percent) and occurs under mild conditions (30° to 100°C).

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