Magnetically recoverable Ni–NiO–bTiO2 heterojunction catalyst for solvent switchable synthesis of amides and amines from nitroarenes

Abstract

The direct synthesis of amides from nitroarenes remains a significant challenge, as existing methods largely rely on multistep sequences, harsh conditions, stoichiometric reagents, and precious metal catalysts, all of which limit efficiency, cost-effectiveness, and sustainability. Moreover, many reported protocols require additives or chromatographic purification, further restricting their practicality and green applicability. Such limitations emphasize the necessity of developing robust, reusable heterojunction catalysts with cooperative active sites to enhance both selectivity and efficiency. Herein, we report a magnetically recoverable Ni–NiO@bTiO₂ heterojunction catalyst for the one-pot, solvent-controlled synthesis of amides or amines from nitroarenes. Ethyl acetate serves dually as a solvent and an acylating agent, enabling tandem hydrogenation–amidation, while switching to 2-propanol selectively yields amines. The unique Ni–NiO–bTiO₂ interfaces in the catalyst, featuring synergistic Ni⁰ active sites and defect-rich bTiO₂ with Ti³⁺ ions and oxygen vacancies, drive high efficiency and selectivity under mild conditions. The methodology is operationally simple, scalable, and eliminates the need for precious metals, additives, or chromatographic purification at a large scale. This demonstrates broad substrate scope, with efficient catalyst recovery via magnetic separation and product isolation through solvent evaporation, further enhancing its green credentials. Green chemistry metrics (AE, RME, E-factor, EcoScale) confirm its environmental sustainability. This work provides a cost-effective, robust, and reusable catalytic platform for sustainable transformations of nitroarenes to amides and amines and has potential for broader application in hydrogenation and tandem reactions.