Chiral bridging ligands

In the first part of this chapter, we will present chiral supramolecular architectures formed from achiral building units that are linked via metal-ligand coordination, where chirality of the assembly results only from the asymmetric arrangement of the molecular components. In the second section, we will deal with chiral assemblies that result from resolved chiral bridging ligands, where chiral information can be transferred to the metal centre and hence a predetermination of the absolute configuration at the metal centre can be achieved and, eventually, the control of the chirality of the supramolecular architecture which can also be defined as stereoselective asymmetric supramolecular assembly . 

A well-organized chiral pore, large enough for a particular guest molecule to access can induce sufficient enantioselection. The chiral bridging ligands of CMOPMs can provide a chiral environment inside the well-organized cavities/ pores, which in principle functions as a chiral selector therefore, they can be considered to possess a built-in chiral selector. Thus in an ideal situation, CMOPMs also have all the qualities to be efficient CSPs for chiral separation processes. 

The Krdhnke synthesis was used as the key step in the preparation of several highly conjugated, chiral bridging ligands such as 198. ... 

Diels-Alder reactions (Scheme 16.16). Recently, they reported that [Rh2(S-BPTPI)4] (56), a new dirhodium(II) carboxamidate complex, that incorporates (S)-3-(benzene-fused-phthalimido)-2-piperidinonate as chiral bridging ligands, is an exceptionally effective Lewis acid catalyst and a more general and highly efficient catalyst for endo- and enantioselective hetero Diels-Alder reactions [17] The catalyst is readily synthesized, air-stable, and easily handled. The present [Rh2(S-BPTPI)4]... 

Figure 5.8 Schematic representation of the three modes for heterogenization of homogeneous catalyst by assembling chiral bridging ligands with metallic ions.

---