Reactions of the μ₃-sulfido triiron cluster [SFe ₃(CO)₉]^2- with functionalized organic halides and mercury salts: Selective reactivity, electrochemistry, and theoretical calculations

When the μ₃-sulfido triiron cluster [SFe₃(CO) ₉]^2- was treated with BrCH₂C(O)OCH₃ in MeCN, the ester-functionalized complex [SFe₃(CO) ₉(CH₂C(O)OCH₃)]^- (1) was obtained. Cluster 1 displays a SFe₃ tetrahedral core with one of the Fe atoms bonded to an ester ligand CH₂C(O)OCH₃. In contrast, when [SFe₃(CO)₉]^2- was treated with dihaloalkanes X(CH₂)_nX′ (X = Cl, X′ = Br, n = 3; X = X′ = I, n = 4) in MeCN, the sulfur-alkylated complexes [X(CH ₂)_nSFe₃(CO)₉]^- (X = Cl, n = 3, 2; X = I, n = 4, 3) were formed, respectively. Clusters 2 and 3 each exhibits a SFe₃ tetrahedral core with the sulfur atom attached to the halide-functionalized alkyl group. Furthermore, the Hg-bridged di-SFe ₃ complex [{SFe₃(CO)₉} ₂(μ₄-Hg)]^2- (4) was isolated from the reaction of [SFe₃(CO)₉]^2- with 2 equiv. of Hg(OAc)₂ in acetone. However, when [SFe₃(CO) ₉]^2- was treated with HgI₂ under similar conditions, the HgI-bridged cluster [SFe₃(CO)₉(μ-HgI)] ^- (5) was produced. In addition, complex 4 could be transformed into complex 3 upon treatment with I(CH₂)₄I in MeCN. Conversely, complex 3 could be reconverted into 4 in the presence of Hg(OAc)₂ in an acetone solution. Clusters 1-5 were fully characterized by spectroscopic methods and single-crystal X-ray analysis. In particular, the nature and selective formation as well as electrochemistry of complexes 1-5, which resulted from the different reactive sites (Fe vs. S atom) of [SFe₃(CO)₉]^2-, were also examined and compared systematically by molecular orbital calculations at the B3LYP level of the density functional theory.