Chiral-at-iron compounds with phosphanes

The design of chiral iron compounds is one of the main current research lines in the field of asymmetric synthesis and catalysis due to the low price, high abundance in the earth's crust, and low toxicity of iron. Because of the interesting electronic and structural properties of phosphanes and their stereochemical rigidity, combining iron with optically pure phosphanes is promising. It has been recently applied in asymmetric transformations. However, the development of chiral iron compounds with achiral phosphanes, which bear the iron atom as the only stereocenter, has been mainly focused on their synthesis and characterization. Although there is a long history and diversity of chemical strategies for the preparation of these chiral-at-iron compounds, in most cases, the stereochemistry (including chirality at metal) of the iron compounds has not been studied in detail, and there is a lack of rational design for targeted chiral compounds and structural analysis. In this review, a description of the synthetic strategies and structure of chiral-at-iron compounds bearing symmetric or asymmetric phosphanes is presented. The structure of the iron compounds is analyzed based on NMR and X-ray diffraction results, with special emphasis on their configurational analysis based on the denticity and hapticity of phosphane ligands, chelate rings and conformations, and the additional donor atoms present in such phosphanes.