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 Damphos 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. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).