Boron-catalysed hydrogenolysis of unactivated C(aryl)–C(alkyl) bonds

The hydrogenolysis of C–C bonds is one of the most important processes in the petroleum industry. These transformations typically rely on heterogeneous catalysts and take place at high temperatures and high pressures with limited selectivity. Employing homogeneous transition metal catalysts, while allowing the hydrogenolysis of C–C bonds to proceed under much milder conditions, is only suitable for substrates containing strained C–C bonds or directing groups. Here we report that a borenium complex can catalyse the selective hydrogenolysis of unstrained C(aryl)–C(alkyl) bonds of alkylarenes in the absence of directing groups at ambient temperature, affording the corresponding alkanes and arenes. Mechanistic studies suggest a reaction pathway that involves a synergistic activation of dihydrogen by the borenium complex and alkylarenes, followed by retro-Friedel–Crafts reaction to cleave the C(aryl)–C(alkyl) bonds. The synthetic utility of this protocol is demonstrated by the conversion of post-consumer polystyrene into valuable benzene and phenylalkanes with mass recovery rates above 90%. Hydrogenolysis of unactivated C(aryl)–C(alkyl) bonds is a challenging task even in the presence of metal catalysts. Now, an approach using a boron catalyst is described that facilitates the hydrogenolysis of alkylarenes under mild conditions, and its utility is demonstrated by degrading polystyrene waste into benzene and phenylalkanes.