Polynuclear manganese complexes of 2,5-dihydroxyterephthalaldehyde (dhterH2) and its Schiff base polymer ligand (PdhterenH2) [Mn(II)(dhter)](n), [Mn(n)(II)(Pdhteren)] and [Mn(n)(III)(Pdhteren)(OAc)(n)] were synthesized. The manganese complexes were characterized by elemental analysis, thermal analysis, IR and EPR spectroscopic techniques. Catalytic epoxidation of olefins with hydrogen peroxide was studied using the above manganese complexes under heterogenized homogeneous reaction conditions in the presence of a base. The effect of imidazole and olefin concentrations on effective oxygen transfer were studied. [Mn(n)(II)(Pdhteren)] and [Mn(n)(III)(Pdhteren)(OAc)(n)] are more efficient than the oxygen-bonded manganese complex [Mn(II)(dhter)](n) for the activation of hydrogen peroxide. (C) 2000 Elsevier Science B.V.