Orientated intercalation of tartrate as chiral ligand to impact asymmetric catalysis

Pre-immobilization of chiral ligands to coordinate with metal centers is one common strategy for the heterogenization of asymmetric metal-complex catalysts. But how the pre-immobilization of chiral ligands made impact on their coordination to metal centers and subsequently asymmetric catalysis has seldom been investigated. Here, in this work. L-tartrate anions as chiral ligands are first intercalated into the interlayer space of Mg/Al layered double hydroxide (LDH) and then in situ coordinated to the Ti (IV) centers. The tartrates are controlled in either perpendicular-standing or fiat-lying arrangement in the interlayer region by altering the solvent for intercalation reaction. The perpendicular-standing interlayer tartrates are found to bear both C-O-Ti and C=O-Ti coordination modes, while the flat-lying interlayer tartrates hold only the C-O-Ti coordination mode. The complex with the Ti (IV) center coordinated to perpendicular-standing interlayer tartrate in both C-O-Ti and C=O-Ti modes not only displays higher catalytic activity in the asymmetric sulfoxidation but also produces higher enantioselectivity for sulfoxide. (C) 2011 Published by Elsevier Inc.