Synergistic Role of Co0 and Lewis Basic Sites for Transfer Hydrogenation of Substituted Nitroarenes by In Situ Hydrogen Generation.

Designing green and efficient methods for synthesizing anilines remains a key challenge in synthetic organic chemistry. Hydrogenation of nitro compounds is one of the most significant and widely employed method for producing functionalized anilines. Consequently, designing catalytic systems capable of hydrogenating nitroarenes under environmentally benign and mild reaction conditions remains a challenge. In this regard, a highly efficient CoAl catalyst has been designed for the hydrogenation of nitroarenes to corresponding amines. Various structural, compositional, and morphological characterizations were done to understand the catalyst's structural and surface properties. The as-synthesized catalyst exhibits excellent activity for the transfer hydrogenation of 1-chloro-4-nitrobenzene to 4-chloroaniline, achieving 98% yield at 60 °C within 1.5 h in ethanol. The developed protocol demonstrated excellent activity for wide range of substituted nitroarenes. Structure-activity relationships of CoAl show that basic sites play a crucial role in the transfer hydrogenation. Furthermore, mechanistic investigations reveal that transfer hydrogenation occurs predominantly via a hydroxylamine-mediated pathway. Moreover, the catalyst maintains good catalytic activity up to four consecutive cycles. This method eliminates the need for high-pressure H2, offering a safe strategy for aromatic amine synthesis. The work demonstrates the potential of earth-abundant, non-noble-metal-based heterogeneous catalysts for hydrogenation reactions under environmentally benign conditions.