Selective Conversion of Nitroarenes to N‐Aryl Hydroxylamines Catalysed by Carbon‐Nanotube‐Supported Nickel(II) Hydroxide

A novel nanohybrid was assembled by a layer‐by‐layer strategy that permitted the immobilization of nickel(II) hydroxide on multi‐walled carbon nanotubes. The heterogeneous catalyst was used for the reduction of a wide variety nitroaromatics to hydroxylamines in a binary solvent mixture (tetrahydrofuran/water), in the presence of sodium borohydride and under mild conditions. The reaction is highly selective as it afforded cleanly the expected aromatic hydroxylamines in the presence of other sensitive groups such as halogens, esters, double bonds or nitriles. The catalyst could also be readily recycled by a simple centrifugation and reused in subsequent reduction reactions with no decrease in catalytic activities, over five cycles. Analysis of the spent catalyst indicated neither alteration in the morphology, metal‐content, nor oxidation state of the carbon nanotube‐supported nickel(II). The catalytic nanohybrid assembly reported in this work thus compares favorably with known systems, as it is very stable, operates at room temperature with limited nickel loading (0.8 mol%), and selectively leads to N‐aryl hydroxylamines without the formation of the corresponding anilines. A novel nanohybrid was assembled by a layer‐by‐layer strategy that permitted the immobilization of nickel(II) hydroxide on multi‐walled carbon nanotubes. The heterogeneous catalyst was used for the selective reduction of a wide variety nitroaromatics to hydroxylamines in the presence of sodium borohydride, under mild conditions.