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

Abstract

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.

Transfer Hydrogenation of Aldehydes and Ketones in Air with Methanol and Ethanol by an Air-Stable Ruthenium–Triazole Complex

“…Catalytic hydrogenation of unsaturated compounds using molecular hydrogen is one of the most fundamental transformations in synthetic chemistry, both in small lab-scale reactions and in large industrial processes. − To avoid the use of expensive high-pressure reactors and drastic reaction conditions for classical hydrogenation, catalytic transfer hydrogenation is considered to be an attractive alternative. − Transfer hydrogenation involves the transfer of a proton and a hydride from the donor molecule to the unsaturated substrate. The sacrificial hydrogen donors, such as formic acid, − is readily available, inexpensive, and much safer to handle.…”

Pd Anchored on a Phytic Acid/Thiourea Polymer as a Highly Active and Stable Catalyst for the Reduction of Nitroarene

“…The use of the CNSP support facilitates the access of the 4-NP substrate to the hydrogen source due to that all reaction components (nitro-arenes, catalyst, and NaBH 4 ) are placed on the support by adsorption. 13 The first step reflects that 4-NP molecules were adsorbed on the surface of the catalyst, which then formed intermediates. Pd−CNSP promptly attracted NaBH 4 as it was put into the system, and NaBH 4 released active H, accompanied with electron transfer and production of BO 2 − and H 2 .…”

“…13 Reduction of nitroarenes to the corresponding amines is one of the most important transformations, which have robust potential applications for the preparation of fertilizing products, additives, pigments, and bioactive compounds. 13,14 However, due to the recognized scarcity challenges and the consequent high cost and poor stability and recyclability of Pd, the wide application of Pd-based catalysts has been hindered. Therefore, extensive efforts have been focused on increasing the active sites, for example, by reducing the size of Pd nanoparticles.…”

“…Palladium-based catalysts, as an important precious metal, play important roles in chemical catalytic reactions, including oxygen reduction, , benzene hydrogenation, Suzuki coupling, nitroarene hydrogenation reduction, , and so on. − Pd-based catalysts usually exhibit excellent catalytic activity for many organic catalytic reactions . Especially, Pd-anchored catalysts have been widely extended in the reduction of nitroarenes via catalytic transfer hydrogenation using hydrides (e.g., NaBH 4 or hydrosilanes) and organic reagents (e.g., alcohol, glycerol, or formic acid) as hydrogen sources . Reduction of nitroarenes to the corresponding amines is one of the most important transformations, which have robust potential applications for the preparation of fertilizing products, additives, pigments, and bioactive compounds. , However, due to the recognized scarcity challenges and the consequent high cost and poor stability and recyclability of Pd, the wide application of Pd-based catalysts has been hindered.…”

“…Especially, Pd-anchored catalysts have been widely extended in the reduction of nitroarenes via catalytic transfer hydrogenation using hydrides (e.g., NaBH 4 or hydrosilanes) and organic reagents (e.g., alcohol, glycerol, or formic acid) as hydrogen sources . Reduction of nitroarenes to the corresponding amines is one of the most important transformations, which have robust potential applications for the preparation of fertilizing products, additives, pigments, and bioactive compounds. , However, due to the recognized scarcity challenges and the consequent high cost and poor stability and recyclability of Pd, the wide application of Pd-based catalysts has been hindered. Therefore, extensive efforts have been focused on increasing the active sites, for example, by reducing the size of Pd nanoparticles.…”