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

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. The disulfide and diselenide bonds of 2,2′‐diheterobis(4,6‐di‐tert‐butylphenol) are reductively cleaved by an iron(II) salt in thepresence of O,X,O donor ligands resulting in the formation of mixed ligand five coordinate iron(III) complexes.