Reduction of Nitroarenes via Catalytic Transfer Hydrogenation Using Formic Acid as Hydrogen Source: A Comprehensive Review

The reduction of nitroarenes to the corresponding aromatic amines is one of the most popular reactions in organic synthesis with significant application in pharmaceutical and manufacture industry. In the last decades, many efforts have been devoted to the design highly effective, chemoselective, low‐cost and eco‐friendly protocols. In this sense, the reduction of nitroarenes via transfer hydrogenation using formic acid as hydrogen source has gained great relevance with tremendous advance over the last year as an attractive and competitive strategy to classical protocols. The efforts have mainly been focused on the discovery of efficient catalyst based on advanced mesoporous support material loaded with transition metals or metallic nanoparticles, the optimization conditions for non‐supported catalyst as well as convenient energy source to achieve an efficient and selective catalytic transfer hydrogenation (CTH) at room temperature. In the present review, several examples of reduction of nitroarenes using formic acid are shown as well as a comprehensive discussion about the role of catalyst, energy source and mechanism of reaction in the transfer hydrogenation process. Catalysts based on noble metals such as palladium, platinum, rhodium or ruthenium or molybdenum have the ability to reduce the nitro group into aromatic systems via catalytic transfer hydrogenation using formic acid as hydrogen source. Specialized construction composed by mesoporous support loaded with nanoscaled transition metals have permitted to extend the metal‐catalyzed CTH using FA to non‐noble transition metals such as cobalt, iron, nickel or copper as well as to noble metals including gold, obtaining excellent results in terms of selectivity, efficacy, reusability, simplicity and green‐chemistry features under room‐temperature conditions in absence of base.