Salan ligands

Organogallium reagents, RsGa, have been added enantioselectively to aldehydes, using TiCl4 as a Lewis acid catalyst, with a chiral salan ligand.258... 

FIGURE 13.7 The divergent connectivity in amine bis(phenolate) ligands bearing a dimethylamino sidearm donor (a), and their isomeric sequential analogues, [ONNO]-type diamine bis(phenolate) (Salan) ligands (b). 

SCHEME 13.2 A one step Mannich-type synthesis is nsed to prepare Salan ligand precursors. 

SCHEME 13.3 Synthesis of Satan polymerization precatalysts, and possible wrapping modes of the Salan ligand around octahedral group 4 metal centers. 

FIGURE 13.9 Representative Salan ligand complexes (Bn = benzyl). 

SCHEME 13.4 Synthesis and polymerization activity of zirconium and titanium catalysts with electron-deficient Salan ligands. 

Inspired by this finding, Katuski further developed a series of structurally tunable di- x-oxo titanium-salan complexes that can be easily prepared and possess amino protons to activate a putative peroxide species. The optimized catalyst (5 mol%) works well for the epoxidation of a variety of unfunctionalized olefins, giving the corresponding epoxides in moderate to good yields with 55-97% ee [262]. The ready availability of the salan ligand and aqueous H2O2 oxidant makes the process very practical for the production of optically active epoxides. 

Scheme 23.5. Asymmetric epoxidation of vinyl arenes with H2O2 mediated by Ti(IV) complex bearing salan ligand.

Scheme 23.23. Asymmetric sulfoxidation of thioethers with H2O2 mediated by a V(IV) complexes with a salan ligand.

Scheme 23.27. Asymmetric sulfoxidation with H2O2 mediated by an Al(III) salan ligand.

Figure 10.6 General structure ofAl complexes featuring SALEM and SALAN ligands (S = spacer).

---