Hydride as a Leaving Group in Nucleophilic Aromatic Substitution

The direct functionalisation of unactivated hydrocarbons remains one of the major challenges in modern chemistry. Here we demonstrate that a simple ruthenium complex with a chelating tBuPN ligand can mediate the nucleophilic aromatic substitution of hydrogen (SNArH) in benzene. Key intermediates were kinetically trapped in low-temperature NMR experiments, providing important insights into the reaction mechanism which is further supported with in-depth DFT studies. These data show that the substitution occurs via an unprecedented mechanism that involves the rear-side nucleophilic addition of the exogenous nucleophile to the ruthenium-bound benzene followed by an intramolecular hydride migration that is facilitated by deprotonation of tBuPN ligand. The broad range of nucleophiles amenable to this reaction, including classical non-nucleophilic bases, showcases the versatility of this reaction and makes it a promising candidate for further developments in the area of SNArH.