GENERAL-SYNTHESIS OF IRON(III) TETRATHIOLATE COMPLEXES - STRUCTURAL AND SPECTROSCOPIC MODELS FOR THE [GE(CYS-S)4] CENTER IN OXIDIZED RUBREDOXIN

A general synthetic route to stable [Fe(III)(SR)4]- complexes is described. The reaction of DMF solutions of [R4N]-[Fe(III)(2,6-dimethylphenolate)4] with excess RSH (R = Me, Et, i-Pr, Ph) gives [R4N][Fe(SR)4] in good yield. [Et4N] [Fe(SMe)4] (1), [(n-Pr)4N] [Fe(SEt)4] (2) and [Et4N] [Fe(SPh)4] (3) were structurally characterized by X-ray crystallography. The [Fe(SR)4]- anions of 1 and 2 possess crystallographic S4 point group symmetry. The [FeS4] core of 2 has nearly perfect T(d) symmetry, whereas the [FeS4] core in 1 has a compressed D2d structure. The [Fe(SPh)4]- anion has approximate S4 SYMMetry with the [FeS4] core compressed along the S4 axis. The existence of the S4 and D2d conformation isomers in tetrahedral [M(SPh)4]n- complexes is discussed. The electronic spectra, H-1 NMR spectra, and the electrochemistry of the [Fe(SR)4]- complexes are reported and compared to those of [Fe(III)(CYS-S)4] centers in proteins.