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%.

Automated summary

The hydrogenolysis of C-C bonds is a crucial process in the petroleum industry, but it often requires high temperatures and pressures with limited selectivity. However, a borenium complex has been discovered to catalyze the selective hydrogenolysis of unstrained C(aryl)-C(alkyl) bonds at ambient temperature without the need for directing groups. Mechanistic studies have revealed that the reaction involves the 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 has been demonstrated by converting post-consumer polystyrene into valuable benzene and phenylalkanes with a mass recovery rate of over 90%.