LAUSR

Abstract Three Mn(III) complexes [Mn(L 1 ) 2 ] (ClO 4 ) 1 , [Mn(L 2 ) 2 ] (ClO 4 ) 2 , [Mn(L 3 ) 2 ] (ClO 4 ) 3 , and one Mn(II) complex [Mn(L 4 ) 2 ] 4 were studied for their efficiency as catalysts for epoxidation of olefins with H 2 O 2 at room temperature and 0 °C in the presence of ammonium acetate-acetic acid or triethylamine-perchloric acid system as co-catalyst/buffer. The complexes were obtained from the reaction of Mn(ClO 4 ) 2 .6H 2 0 with NNO tridentate Schiff base ligands HL 1 -HL 4 synthesized from the condensation reaction of 2-(2-aminoethyl)pyridine and 2-hydroxybenzaldehyde (HL 1 ), 5-chloro-2-hydroxybenzaldehyde (HL 2 ), 5-methoxy-2-hydroxybenzaldehyde (HL 3 ), or 5-nitro-2-hydroxybenzaldehyde (HL 4 ) respectively. The complexes were characterized by spectroscopic techniques as well as by single crystal X-ray diffraction analysis. Electronic effect of the substituents on epoxide yield was also investigated. The crystal structures of complexes confirm coordination of the manganese ion to the ligands through the NNO atoms of the ligands. The spectral changes observed as a function of time for the reaction of the complexes with aqueous (30%) hydrogen peroxide indicates possible formation of an intermediate product; hydroperoxo-complex implicated in the epoxidation reaction. The complexes catalyzed epoxidation of cyclohexene with low yield at room temperature but higher yield at 0 °C in the order complex 3 lower than 1, 1 lower than 2, with the Mn(II) complex 4 recording highest epoxide yield of 9% with turnover of 2.25 at room temperature and yield of 58% with turnover of 14.5 at 0 °C in the presence of ammonium acetate-acetic acid system/ buffer. With the triethylamine-perchloric acid system/buffer, epoxide yield of 46% and turnover of 11.5 was recorded at room temperature while 44% with turnover of 11.0 was obtained at 0 °C for complex 4 .