Exclusive catalytic hydrogenation of nitrobenzene toward p-aminophenol over atomically precise Au36(SR)24 clusters

Abstract

Despite the advances in devising green methodologies for selective hydrogenation of nitrobenzene toward p-aminophenol, it is still difficult to realize p-aminophenol as the exclusive product in heterogeneous metal catalysis, as the excessive hydrogenation of nitrobenzene usually results in the aniline byproduct. Herein we report that a metal cluster containing 36 gold atoms capped by 24 thiolate ligands provides a unique pathway for nitrobenzene hydrogenation to achieve a p-aminophenol selectivity of ∼100%. The gold cluster can efficiently suppress the over-hydrogenation of amino groups via hydroxyl rearrangement with the aid of water and sequentially the proton transfer promoted by acid toward p-aminophenol. More notably, remarkable catalytic performances can be extended to clusters with similar structures such as Au₂₈(SR)₂₀ and Au₄₄(SR)₂₈, where only an atomic layer change of 2.1 Å thickness in the Au₃₆(SR)₂₄ cluster can tailor the proton affinity for the amino group of the key intermediate phenylhydroxylamine, thereby altering the activity while the p-aminophenol selectivity remained.