Chiral Iron Complexes in Asymmetric Organic Transformations

Transition metal chiral catalysts can feature metal stereocenters in different coordination geometries. In the case of iron, both octahedral and tetrahedral geometries possessing a chirotopic iron atom have been synthesized and tested in stereoselective organic transformations. The configurational stability of these complexes, which in some cases is hampered by decomplexation and recomplexation of labile ligands, is achieved by the use of multidentate ligands in octahedral complexes, and of cyclopentadienyl anions (half sandwich complexes) in the case of tetrahedral structures. The use of octahedral iron complexes featuring configurationally stable iron stereocenters is reviewed in highly enantioselective reductions (hydrogenation and transfer hydrogenation of ketones) and oxidations (cis-dihydroxylation of alkenes, epoxidation, sulfoxidation), while the use tetradentate iron complexes is described in C−C bond-forming reactions and reductions.