Iron is a popular target of research in catalytic processes, because of its low cost and low toxicity compared to other transition metals. Asymmetric transfer hydrogenation methods using iron have already been developed. In terms of reaction rate and selectivity, however, they are inferior to catalysts based on precious metals. Within the EU-funded project ASYMM.FE.SUSCAT (Sustainable asymmetric catalysis with iron), scientists prepared an air-stable iron complex suitable for biologically relevant amines. Amines are among the most valuable compounds in organic chemistry and widely used in pharmaceuticals and agrochemicals. The so-called Knölker complex, designed for the selective synthesis of chiral animes, operates through the borrowing hydrogen methodology. This hydrogen auto transfer process combines the advantages of transfer hydrogenation with additional transformations. During transfer hydrogenation, the ASYMM.FE.SUSCAT iron complex is highly stable and remains inert under different reaction temperatures. Moreover, the hydrogenation process is irreversible, resulting in the complete shift of the reaction equilibrium to the product. Using enantiopure amines and alcohols containing a stereogenic centre adjacent to the hydroxyl ion or amidogen, scientists produced either chiral animes or a racemic mixture. Specifically, a broad range of chiral animes was alkylated by aliphatic alcohols with reaction yield as high as 90 %. Another important ASYMM.FE.SUSCAT achievement was the use of copper-based catalysts in the hydrogenation of biomass-derived 5-hydroxymethylfurfural and the synthesis of benzimidazoles from aromatic diamines or nitroanilines. Copper proved to be a promising alternative to precious metals. The new catalytic methods should enable waste-free conversion of renewables to give access to a variety of commodities or fine chemicals. The structural diversity of biomass-derived substrates is a challenge, but also a key opportunity for the understanding of iron as well as copper catalysis.
Catalysis, iron complexes, asymmetric transfer hydrogenation, precious metals, ASYMM.FE.SUSCAT