Synthesis of catalytically active polymer-bound Mn(III) salen complexes for enantioselective epoxidation of styrene derivatives

Abstract

Catalytically active metal-complexing polymer-containing chiral Mn(III) salen moieties derived from (1 R, 2 R)-(−)-diphenylethylenediamine, (1 S, 2 S)-(+)-cyclohexanediamine, and ( S)-(+)-diaminopropane with α-naphthyl salicylaldehyde anchored to the polymeric matrix obtained from styrene-4-vinyl pyridine-divinyl benzene (PVPD) have been synthesised. These catalysts were used for enantioselective epoxidation of styrene and substituted styrenes, viz. 4-chloro-, 4-methyl and4-nitrostyrene using iodosyl benzene as terminal oxidant by GLC. The enantiomeric excess of the resulting epoxide was determined by GLC using chiral capillary column or by 1H-NMR using chiral-shift reagent Eu(hfc) 3. Each catalyst/substrate combination was examined under epoxidation condition and the results for catalysts 1–3 are presented as Hammet plots. A mechanism involving formation of an Mn-oxo complex and oxygen transfer from a reactive Mn-oxo intermediate to styrene was also proposed for the reaction. These catalysts can be recycled at least ten times without loss of its activity.