IntroductionFerrocene as a (at the time rather exotic) backbone for chiral ligands was introduced by Kumada and Hayashi [1] based on Ugi's pioneering studies related to the synthesis of enantiopure ferrocenes ( Fig. 25.1). Ppfa, as well as bppfa and bppfoh, proved to be effective ligands for a variety of asymmetric transformations. From this starting point, several ligand families with a range of structural variations have been developed during the past few years. In this chapter we will describe effective ligand structures developed over time, the main focus being on diphosphine derivatives ( Fig. 25.2) and their application to the hydrogenation of alkenes. Three recently published reviews cover some of the same area, but from slightly different points of view. Colacot and Barbaro et al. [2] presented general overviews on ferrocene-based chiral ligands and their application to various asymmetric transformations, while Blaser et al. [3] and Tang and Zhang [4] reviewed the recent progress in the application of diphosphines for the enantioselective hydrogenation. These reviews can serve to put the present account into a broader perspective.This chapter is organized according to the position of the phosphine groups P, as depicted in Fig. 25.2. It is important to realize that many of the ligands described here have both planar (C p ring with two different substituents) as well 833 The Handbook of Homogeneous Hydrogenation. Edited by J. G. de Vries and C. J. ElsevierFig. 25.1 Structures of Ugi's amine and the first ferrocene-based chiral phosphine ligands.