Unsymmetrical 1,1′‐Bidentate Ferrocenyl Ligands

Abstract

This chapter focuses on the preparation of enantiopure 1,1 0 -unsymmetrically disubstituted ferrocenes and their applications in asymmetric catalysis. Notably, Gibson, Long, and coworkers have documented a comprehensive review on the synthesis and catalytic applications of unsymmetrical ferrocene ligands [1]. Enantiopure 1,1 0 -bidentate ferrocenyl ligands attracted much attention soon after the discovery of ferrocene, mainly due to their unique rigid binding mode and relatively straightforward synthesis. Even today, 1,1 0 -bidentate ferrocenes still serve as an important scaffold for the design of new chiral ligands. It should be noted that the symmetrical 1,1 0 -bidentate ferrocenyl ligands, a very important class of this family, are discussed in Chapter 7. In this chapter, in addition to those having two different substituents at the 1,1 0 -positions of ferrocene I, the scope of ferrocenyl ligands will also cover unsymmetrical ferrocenyl ligands bearing identical coordination groups at the 1,1 0 -positions of ferrocene (II), for example, L1a [(R,Sp)-BPPFA] (Figure 8.1).Due to the ready availability of BPPFA and its close analogs, they have been used for many catalytic asymmetric reactions. However, the corresponding work in which BPPFA and its close analogs were simply screened and unable to afford the optimal result will not be discussed in detail. This chapter will be divided into several parts based on the reaction type. Palladium-Catalyzed Asymmetric Allylic Substitution ReactionPalladium-catalyzed allylic substitution reactions have been used extensively in asymmetric carbon-carbon and carbon-heteroatom bonds formation to provide chemo-, regio-, diastereo-, and enantioselectivity [2]. The enantioselective version of this reaction has been demonstrated successfully in organic synthesis, including the Chiral Ferrocenes in Asymmetric Catalysis. Edited by Li-Xin Dai and Xue-Long Hou