Optically Active Phospholanes as Substituents on Ferrocene and Chromium‐Arene Complexes

An improved synthesis of (R,R)‐ and (S,S)‐hexane‐2,5‐diol is presented. The (S,S)‐derivative was converted into a cyclic sulfate, which on treatment with NaPH2 in liquid ammonia ultimately gave the secondary (R,R)‐2,5‐dimethylphospholane. This phospholane can be introduced into the side chain of chiral tricarbonylchromium and ferrocene derivatives to give new bidentate ligands of the Josiphos and Daniphos type. Both the ferrocene‐ and tricarbonylchromium‐based diphosphanes have been characterized by X‐ray diffraction analysis. A discussion of their structural features is included. The new ligands were successfully applied to the enantioselective hydrogenation of itaconic acid esters. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)