Study On Chelate And Substituent Effects Of 8-quinonlionlato Manganese Complexes For Epoxidation Of Olefins

Epoxidation of olefns is a very outstanding transformation in organic synthesis,since the reaction products,epoxides,can be easily converted to large variety of compounds.In terms of atom efficiency,aqueous hydrogen peroxide would undoubtedly be the ideal oxidant since it produces water as the sole by-product and can therefore be classified as the ultimate green oxidant.Moreover,for industrial applications,the development of epoxidation systems using cheap and nontoxic metal complexes as catalysts is significant.The molecular switches like 8-quinolinolato manganese(â…¢) complexes have been proven to be very effective catalysts to catalyze this reaction.In order to gain greater understanding of these epoxidation systems,we designed and synthesized a series of 8-quinolinolato manganese complexes,and investigated their catalytic efficiency in catalyzing the epoxidation of olefins with H₂O₂. Our works are summarized in details as follows:1) we designed and synthesized a series of 8-quinolinolato manganese complexes,and investigated the of chelate and substituent effects of 8-quinoliolato manganese complexes on their catalytic performances for epoxidation of styrene with aqueous H₂O₂.The results showed that hexadentate Q₃Mn^â…¢complexes own the higher catalytic efficiency and better stability than the corresponding tetradentate Q₂Mn^â…¡ones,which should be due to their distortion effect.Moreover,the halogenated Q₃Mn^â…¢complexes show the enhanced distortion effect, which can lead to the significant improvement on catalytic activity.2) 8-quinolinolato manganese complexes have been successfully grafted onto chloromethyl polystyrene resin by Friedel-Crafts reaction and performed for the epoxidations of olefins with aqueous H₂O₂ in water-acetone media containing ammonium acetate(NH₄OAc) and acetic acid(HOAc).It was found that the grafted catalysts showed good catalytic efficiency and better stability.3) We investigated the catalytic performance of such Q₃Mn^â…¢complexes for epoxidation of olefins with H₂O₂ in acetone medium without any additive,especially the effect of water on the epoxidation of styrene.The results showed that the Q₃Mn^â…¢complexes gain the higher catalytic efficiency in this system.