Binuclear oxo-bridged iron(III) complexes of chiral tetradentate ligands

摘要

The syntheses and characterization of a series of binuclear iron(III) complexes of the chiral ligands N,N'-bis(2-pyridylmethyl)-(-)(D)-1,2-propanediamine, bispic(-)pn, C15H20N4, N,N'-bis(2-pyridylmethyl)-(-)(D)-1,2-cyclohexanediamine, bispic(-)chxn, C18H24N4, and N,N'-bis(2-pyridylmethyl)-N,N'-dimethyl-(-)(D)-1,2-cyclohexanediamine, bispicMe(2)(-)chxn, C20H28N4, are described. The mu-oxo-mu-carbonatodiiron(III,III) complex, [{Fe(bispicMe(2)(-)chxn)}(2)(mu-O)(mu-CO3)] (ClO4)(2) . 4H(2)O, [Fe2C41H56N8O4] (ClO4)(2) . 4H(2)O (1), crystallizes in the space group P2(1)2(1)2(1) of the orthorhombic system with four binuclear species in a cell of dimensions a = 14.066(3), b = 18.405(4), c = 19.164(4) Angstrom. The structure was refined to a final R-factor of 0.0941 based on 2045 observed independent reflections. The mu-oxo-mu-bicarbonatodiiron(III,III) complex, [(Fe(bispicMe(2)(-)chxn)}(2)(mu-O)(mu-HCO3)] (ClO4)(3) . H2O, [Fe2C41H57N8O4](ClO4)(3) . H2O (2), crystallizes in the space group I4(1)22 of the tetragonal system with eight binuclear species in a cell of dimensions a = 20.527(3), c = 24.499(5) Angstrom. The structure was refined to a final R-factor of 0.0527 based on 2604 observed independent reflections. The mu-oxo-mu-acetatodiiron( (III,III) complex, [(Fe(bispicMe(2)(-)chxn)}(2)(mu-O)(mu-OAc)](ClO4)(3) . H2O, [Fe2C42H59N8O3](ClO4)(3) . H2O (3), is isomorphous with 2 with eight binuclear species in a cell of dimensions a = 20.527(3), c = 24.377(5) Angstrom. The structure was refined to a final R-factor of 0.0673 based on 1954 observed independent reflections. The complexes contain bent Fe-O-Fe units with bridging Fe-O-Fe angles of 124.2(8), 130.7(4), and 130.6(6)degrees and associated Fe ... Fe separations of 3.212(5), 3.283(2), and 3.287(5) Angstrom for 1, 2, and 3, respectively. The ligand binds the iron centers in cis-alpha fashion in all three complexes. The complexes exhibit electronic absorption bands similar to methemerythrin enzymes in the 400 to 550 nm region, but they do not exhibit negative circular dichroism spectral features like the enzymes. Cyclic voltammograms of the complexes reveal a reversible one-electron reduction, corresponding to the (FeFeIII)-Fe-III --> (FeFeIII)-Fe-II odor process, at -0.43, + 0.08, and + 0.12 V versus an Ag/AgCl reference electrode for 1, 2, and 3, respectively. Complexes 2 and 3 also exhibit an irreversible reduction peak at -0.86 and -0.83 V, respectively. (C) 1998 Elsevier Science S.A. All rights reserved. [References: 29]