An unconventional direct path for the chemoselective hydrogenation of nitroarenes over a metal-free catalyst

Abstract

In recent years, significant efforts have been devoted to the fabrication of heteroatom-doped carbon materials as ecofriendly catalysts to replace metal-based catalysts employed in the hydrogenation of nitroarenes. However, the reaction pathway of metal-free catalysts has not been thoroughly studied. In this study, nitrogen-doped hollow hierarchical porous carbon materials have been successfully prepared. The porous nitrogen-doped carbon was prepared by carbonizing at 900°C (PNC-900) and exhibited an exceptional catalytic performance in the chemoselective hydrogenation of nitroarenes with high tolerance to various substrates under mild reaction conditions. The analysis of the experimental results and characterizations, revealed that graphitic N species were the primary catalytic active sites and played a crucial role in efficient hydrogenation. The reaction followed a special direct path in the hydrogenation of nitrobenzene (NB) owing to the absence of nitrosobenzene (NSB) as an intermediate, which was markedly different from the other metal-free catalysts. Moreover, the PNC-900 catalyst exhibited excellent reactivity and selectivity even after six cycling tests, thus demonstrating unconventional high performance in terms of both recyclability and stability.