Salan type ligand

A remarkable and unprecedented stereocontrol switch has also been achieved in the ROP of rac-lactide initiated by aluminum complexes supported by tetradentate aminophenoxide salan-type ligands (Scheme 17). Thus, apart from the well-controlled and living character of these ROP reactions, it was found that the... 

Group 4 metals have also been used widely in conjunction with salen-type ligands (Figure 25). In 2006 Gregson et reported several chiral and achiral titanium salen alkoxide complexes for the ROP of lactide. All catalysts reported were modestly active and heteroselective (P 0.51-0.57). Several achiral Ti and Zr salan catalysts were reported by Gendler et for melt polymerization of lactide. While no stereoselectivity has been reported for either system, the Zr complexes were more active towards lactide ROP than the Ti analogs. 

The utilization of organogallium as an alkylation reagent for asymmetric alkylation of aldehydes has been realized by using titanium complex as a chiral Lewis acid catalyst. The titanium catalyst was obtained by the reaction of TiCU with a salan [N,N-bis(o-hydroxybenzyl)-l,2-diaminoethane] type ligand. Moderate to good chemical yields were obtained with up to 84% ee [53] (Scheme 14.8). 

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. 

---