The two-step one-pot oxidative decarbonylation of [Fe2(S2C2H4)(CO)4(PMe3)2] (1) with [FeCp2]PF6, followed by addition of phosphane ligands, led to a series of diferrous dithiolato carbonyls 2–6, containing three or four phosphane ligands. In situ measurements indicate efficient formation of 12+ as the initial intermediate of the oxidation of 1, even when a deficiency of the oxidant was employed. Subsequent addition of PR3 gave rise to [Fe2(S2C2H4)(μ-CO)(CO)3(PMe3)3]2+ (2) and [Fe2(S2C2H4)(μ-CO)(CO)2(PMe3)2(PR3)2]2+ (R=Me 3, OMe 4) as principal products. One terminal CO ligand in these complexes was readily substituted by MeCN, and [Fe2(S2C2H4)(μ-CO)(CO)2(PMe3)3(MeCN)]2+ (5) and [Fe2(S2C2H4)(μ-CO)(CO)(PMe3)4(MeCN)]2+ (6) were fully characterized. Relevant to the Hred state of the active site of Fe-only hydrogenases, the unsymmetrical derivatives 5 and 6 feature a semibridging CO ligand trans to a labile coordination site.