Iron(II)‐Mediated Reductive Cleavage of Disulfide and Diselenide Bonds: Iron(III) Complexes of Mixed O , X , O and O , X (X = S, Se) Donor Ligands

Abstract

The syntheses and characterization of a methoxo-bridged diiron(III) complex, [Fe2LSe2(μ-OCH3)2(CH3OH)2] (1), and three mononuclear iron(III) complexes Bu4N[FeLSe2] (2), Bu4N[FeLSe′LSe] (3) and Bu4N[FeLS′LS] (4) [H2LSe = 2,2′-selenobis(4,6-di-tert-butylphenol), H2LS = 2,2′-thiobis(4,6-di-tert-butylphenol), H2LSe′ = 3,5-di-tert-butyl-2-hydroxyselenophenol, and H2LS′ = 3,5-di-tert-butyl-2-hydroxythiophenol] are discussed. The single crystal structure of 1·7CH3OH, as determined by XRD, reveals an asymmetric Fe2O2 core in which the two iron and two methoxo oxygen atoms constitute a perfect planar atomic arrangement. Complex 1 exhibits a moderate antiferromagnetic exchange coupling (J = –13.2 cm–1) that operates between the two high spin iron(III) centers (SFe = 2.5) with a resulting St = 0 ground state, while 2 is a six coordinate mononuclear high spin iron(III) complex. The mixed ligand complexes 3 and 4 are formed during the reaction of a tridentate O,X,O ligand (X = S, Se) with iron(II) salts in the presence of either the H2LSe–Se or H2LS–S ligand [H2LSe–Se = 2,2′-diselenobis(4,6-di-tert-butylphenol), and H2LS–S = 2,2′-dithiobis(4,6-di-tert-butylphenol)] in an inert atmosphere, whereby iron(II) is oxidized to iron(III) and the disulfide or diselenide bonds are reductively cleaved. The temperature-independent magnetic moment values of 3 and 4 indicate that the complexes contain mononuclear high spin iron(III) centers. The crystal structure of 3 confirms that a reductive Se–Se bond cleavage with concomitant formation of a five coordinate trigonal bipyramidal anionic iron(III) complex, [FeLSe′LSe]–, has occurred. It is proposed that the iron(II) ions take part in the electron-transfer reaction associated with the reductive cleavage of the disulfide and diselenide bonds.