Cobalt nanoclusters coated with N-doped carbon for chemoselective nitroarene hydrogenation and tandem reactions in water

Abstract

The development of active and selective non-noble metal-based catalysts for the chemoselective reduction of nitro compounds in aquo media under mild conditions is an attractive research area. Herein, the synthesis of subnanometric and stable cobalt nanoclusters, covered by N-doped carbon layers as core–shell (Co@NC-800), for the chemoselective reduction of nitroarenes is reported. The Co@NC-800 catalyst was prepared by the pyrolysis of the Co(tpy)₂ complex impregnated on Vulcan carbon. In fact, the use of a molecular complex based on six N–Co bonds drives the formation of a well-defined and distributed cobalt core–shell nanocluster covered by N-doped carbon layers. In order to elucidate its nature, it has been fully characterized by using several advanced techniques. In addition, this as-prepared catalyst showed high activity, chemoselectivity and stability toward the reduction of nitro compounds with H₂ and under mild reaction conditions; water was used as a green solvent, improving the previous results based on cobalt catalysts. Moreover, the Co@NC-800 catalyst is also active and selective for the one-pot synthesis of secondary aryl amines and isoindolinones through the reductive amination of nitroarenes. Finally, based on diffraction and spectroscopic studies, metallic cobalt nanoclusters with surface CoN_x patches have been proposed as the active phase in the Co@NC-800 material.