Synthesis of chiral periodic mesoporous silicas incorporating tartrate derivatives in the framework and their use in asymmetric sulfoxidation

The synthesis of chiral periodic mesoporous organosilicas (ChiMO) of MCM-41 type using a bis-silylated tartramide derived from L-(+)-dimethyl tartrate (Sharpless and Kagan ligand) has been studied. The ChiMO materials were characterized by powder XRD, TEM, and nitrogen adsorption-desorption measurements, verifying their successful preparation. The evidence of the covalent bonding between the organic chiral precursor and the inorganic silica framework structure was confirmed by C-13 and Si-29 NMR solid state measurements. The synthesized chiral PMO was found to catalyze the asymmetric oxidation of thioanisole with good sulfoxide yield and moderate enantioselectivity. Reutilization of the solid chiral ligand led to similar optical yields to that obtained with the fresh ChiMO, revealing the true heterogeneous nature of the immobilized tartrate derivative.