A new series of anionic complexes of iron tetracarbonyl monofunctionalized with the ligand [RS− 1, [RSFe(CO)4− ] (R = Ph, Et, Me, H), have been synthesized and characterized. The compound [PPN] [PhSFe(CO)4] was formed in the reaction of [PPN] [HFe(CO)4] and PhSSPh. The [PhSFe(CO)4−] anion was characterized by X-ray diffraction as its [PPN+] salt and found to be a typical trigonal-bipyramidal complex in which the phenylthiolate ligand occupies an axial position with a Fe-S bond distance of 2.332 (5) Å and ΔFe-S-C(Ph) - 111.3 (6)°. The salt crystallized in the orthorhombic space group Pbc21, with a = 9.529 (4) Å, b = 21.493 (9) Å, c - 20.185 (9) Å, V = 4134 (3) Å3, and Z = 2. Other members of the series of complexes, [RSFe(CO)4− ], were best obtained by ligand exchange of [RS−] and the labile thioether complex (PhSMe)Fe(CO)4. The latter was produced from the low-temperature alkylation of the [PhSFe(CO)4− ]. Protonation of the thiolates (R = Ph, Et, Me, H) ultimately leads to formation of H2 and Fe2(μ-SR)2(CO)6; however, the intermediate thiol, (RSH)Fe(CO)4, could be observed at -78 to -40 °C for R = Et, Me. The PhSH and HSH derivatives were unstable even at -78 °C. © 1989, American Chemical Society. All rights reserved.