Bootstrap Synthesis Revisited: A Solid, Cobalt-Derived Catalyst Enables the Hydrogenation of N═N Bonds to Afford Anilines

Abstract

We communicate a solvent-free and low-waste method for the fabrication of a heterogeneous, Co-based hydrogenation catalyst. Careful pyrolysis of a solid [Co(acac)2]/phthalocyanine/Vulcan mixture (acac = acetylacetonate) under an argon atmosphere furnishes a ready-to-use, catalytically active material that can be handled without any protection from air. The composite so obtained was then used in the pressure hydrogenation of azo dyes (60 °C, 50 bar H2) to yield the corresponding aniline derivatives, without any additive. The potential of the catalyst to design a bootstrap synthesis approach of aromatic amines, i.e., their generation from within themselves, by way of reduction of symmetric azo compounds is explored herein, too. To further demonstrate the practicality of the introduced catalyst, we also applied it to the hydrogenation of nitroarenes as another means for the production of arylamines. In all investigated cases, the NO2 motif was neatly and selectively converted into the desired NH2 group under very mild reaction conditions (room temperature, 20 bar H2) and, again, without the need for any auxiliary reagents.