Regioselectivity-Switchable Hydroarylation of Styrenes

Cobalt−phosphine and cobalt−carbene catalysts have been developed for the hydroarylation of styrenes via chelation-assisted C−H bond activation, to afford branched and linear addition products, respectively, in a highly regioselective fashion. Deuterium-labeling experiments suggested a mechanism involving reversible C−H bond cleavage and olefin insertion steps and reductive elimination as the rate- and regioselectivity-determining step.