Synthesis and characterization of mono- and bi-metallic Mn(III) complexes containing salen type ligands

A mononuclear complex 1, of Mn(III) with a Schiff-base ligand L [L = N,N'-e thylenebis(3-formyl-5-methylsalicylaldimine)] has been synthesized and stru cturally characterized. A series of binuclear complexes, MnML'Cl(x)solv(y) [M = Zn(II), Cu(II), Ni(II), Co(II), Fe(III), and Mn(III); x = 3 or 4 depen ding on the oxidation state of M; L' is the aniline condensation product of L; y = 1, 2 or 3 and solv = H2O or CH3OH] have been prepared by the reacti on of 1, aniline and M(II/III) chloride with a 1 : 3 : 1.2 molar ratio in m ethanolic media. These bimetallic complexes were characterized by elemental analyses, UV-Vis and IR spectroscopies, magnetic susceptibilities and ther mogravimetric analyses. The results of magnetic susceptibility measurements at 300 K indicate that all the metal ions are in their high spin states. T he catalytic properties of these complexes for epoxidation of alkenes have been investigated using PhIO as a terminal oxidant. The binuclear Mn(III) c omplexes are less efficient epoxidation catalysts than the mononuclear Mn(I II) complex, 1. The reduced activities of the bimetallic complexes may be d ue to both the low rates of formation of a Mn(V)O intermediate and the tran sfer of oxygen from this intermediate to the alkene. Furthermore, the bimet allic complexes also transformed into a catalytically inactive species in t he presence of PhIO as indicated by UV-Vis spectroscopic studies.