SYNTHESIS, CHARACTERIZATION AND CATALYTIC PROPERTIES OF MANGANESE(III) SCHIFF-BASE COMPLEXES

The syntheses and spectral and electrochemical characterization of five manganese(III) complexes with Schiff base ligands are described. The crystal structure of the complex [Mn(SALENCY)(H2O)(CH3CH2OH)]ClO4 where SALENCY, C20H20N2O22--, is the dianion of the product formed from the condensation of two moles of salicylaldehyde with one mole of 1,2-diaminocyclohexane, has been established by X-ray diffraction techniques. The complex crystallizes in the space group P21/n of the monoclinic system with four molecules in a cell of dimensions a=11.678(3), b=15.654(3), c= 13.356(2) Å, and β=93.00(2)°. The structure was solved by direct methods and refined by least-squares techniques to a final value of the weighted R factor of 0.0437 based on 1484 independent observed reflections. The complex is roughly octahedral, the Schiff base ligand occupying four basal sites while the axial sites are occupied by one water molecule and one ethanol molecule. The complex [Mn(TETRAMESALEN)Cl], where TETRAMESALEN, C20H22N2O22-, is the dianion of the product formed from the condensation of two moles of 2′-hydroxy- 5′-methylacetophenone with one mole of 1,2- diaminoethane, crystallizes in the monoclinic space group P21/c with four molecules in a cell of dimensions a=11.009(4), b=12.459(3), c=13.967(4) Å, β=97.25(3)°. The structure was solved by direct methods and refined to a final R factor of 0.0535 based on 2342 observed independent intensities. The complex is tetragonal pyramidal, the Schiff base ligand occupying the basal sites while the chloride is axial. The complex [Mn(MEPHSALEN)(C2H5OH)2]- ClO4, where MEPHSALEN, C30H26N2O22--, is the dianion of the product formed from the condensation of two moles of 2′-hydroxy- 5′-methylbenzophenone with one mole of 1,2-diaminoethane, crystallizes in the triclinic space group P1 with four molecules in a cell of dimensions a=9.492(3), b=17.404(6), c= 21.265(9) Å, α=86.60(3), β=88.57(3), γ= 86.34(3)°. The data for this complex are of lower quality than those obtained for the other two complexes, but the structure has been refined to a final value of 0.090 based on 1263 independent intensities. There are two crystallographically independent molecules in the cell, but the geometry of each is substantially similar. In each case, the manganese atom is six-coordinate, the base of the pseudo-octahedron being occupied by the Schiff base ligand while the axial sites are occupied by ethanol ligands. The two six-coordinate complexes (SALENCY and MEPHSALEN) are very effective at catalyzing the epoxidation of cyclohexene by iodosobenzene, while the five-coordinate complex yields both epoxide and cyclohexenol. © 1990.