Reactive & Functional Polymers, Vol.34, No.2, 153-160, 1997
Synthesis of catalytically active polymer-bound Mn(III) salen complexes for enantioselective epoxidation of styrene derivatives
Catalytically active metal-complexing polymer-containing chiral Mn(III) salen moieties derived from (1R, 2R)-(-)-diphenylethylenediamine, (1S,2S)-(+)-cyclohexanediamine, and (S)-(+)-diaminopropane with cu-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- and 4-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 H-1-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.
Keywords:SCHIFF-BASE COMPLEXES;TWIN-CORONET PORPHYRINS;ASYMMETRICEPOXIDATION;OLEFINS;HYDROXYLATION;CATALYSTS;ALKENES