Abstract: Highly enantioselective epoxidation of olefins (with up to 99.8 % ee) and oxidation of thioethers (up to 98.5 % ee) with “green” H2O2 on novel chiral titanium(IV) salan and salalen complexes is reported. The effects of steric bulk and electronic properties of chiral ligands on the enantioselectivity of oxidations have been examined. Mechanistic studies reveal distinct mechanisms operating in those processes: stepwise mechanism for epoxidations and concerted one for sulfoxidations. The epoxidation on Ti-salan complexes is rate-limited by coordination of the olefin to the electrophilic titanium peroxo active species, while sulfoxidation on Ti-salalen complexes is rate-limited by generation of the titanium peroxo species upon reaction of the catalyst with H2O2. For the first time, non-linear temperature dependence of enantioselectivity (isoinversion behavior) has been documented for the asymmetric sulfoxidation reactions, with Tinv of 273…283 K, which temperature range may be recommended for preparative catalytic sulfoxidations

Cite: Talsi E.P. , Bryliakov K.P.
Highly Enantioselective Oxidation of Olefins and Thioethers with H2O2 Mediated by Chiral Titanium(IV) Complexes
EuropaCat-XII: 12th European Congress on Catalysis “Catalysis: Balancing the use of fossil and renewable resources” 30 Aug - 4 Sep 2015