The perfluorosulfanylvinyldiiron(I) complex [_Fe(CO)3₂_μ-C(SMe)(CF3)C(CF2)_] 1 reacted with tertiary phosphanes [L = PPh3 or P(OMe)3] in dichloromethane or chloroform at 6°C to give high yields of cycloferrathiapentadiene iron clusters. When the nucleophile was PPh3, the salt 2 was obtained: formally, a fluoride-ion transfer between two molecules of 1 generates the anion [_Fe(CO)3₂_μ-C(CF3)C(CF 3)SMe_]- and addition of PPh3 at two separate sites produces the counter cation [(Ph3P)(OC)2Fe_μ-CFC(PPh3)C(CF 3)SMe₋Fe(CO)3]+. In contrast, with P(OMe)3 the neutral derivative [_Fe(CO)3₂_μ-CFC[PO(OMe)2]C(CF 3)SMe_] 4 was formed. Thermally induced C-F bond activation is a feature of these reactions. All the reaction products have been characterized by elemental analysis and IR, 1H, 19F, 31P and 13C NMR spectroscopy. The solid-state structure of [(Ph3P)(OC)2Fe_μ-CFC(PPh3)C(CF 3)SMe_Fe(CO)3][_Fe(CO)3_ 2_μ-C(CF3)C(CF3)SMe_] 2 has been established by single-crystal X-ray analysis. The Fe-Fe bond in the cation [2.716(2) Å] is appreciably longer than the corresponding bond in the anion [2.570(2) Å]. Possible routes to the formation of 2 and 4 have been investigated. The conversion of 1 into 4 has been shown to involve an intermediate 3 which has been fully characterized by 19F, 31P and 13C NMR spectroscopy.