Fluorous biphasic oxidation of sulfides catalysed by (salen)manganese(III) complexes

Abstract

Abstract Quadridentate Schiff base ligands derived from 1,2-diamines and fluorous derivatives of salicylaldehyde were prepared and the corresponding manganese(III) complexes were tested as catalysts in the selective oxidation of alkyl aryl sulfides with PhIO. Complexes bearing two fluorinated ponytails were soluble in standard organic solvents and were used under classical homogeneous conditions, whereas heavily fluorinated complexes could be used in a CH3CN/perfluorooctane biphasic system. In both cases, sulfoxides were obtained as the main products, together with variable amounts of sulfones (≤10%), depending on the nature of the substrate and the catalyst. When reactions were carried out under fluorous biphasic (FB) conditions, the selectivity for sulfoxides was improved and the catalyst could be easily recovered by simple phase separation and reused up to four times. Despite their good chemoselectivity, catalytic efficiency and recyclability, chiral fluorous (salen)manganese(III) complexes showed low enantioselectivities in preliminary experiments run under fluorous biphasic conditions.