A Deeper Insight in Solutions Containing the Hypothetical Labile Complex Species “Fe(CO)4THF”

In the literature it was proposed that the treatment of [Fe2(CO)9] in THF resulted, during dissolution, in deep red solutions which should presumably contain labile complexes “Fe(CO)4THF”. This was supported by the fact that such solutions afforded, in the presence of N‐donor ligands like pyridine (py) or pyrazine (pz), metal carbonyl complexes of the formula [Fe(CO)4(py)] and [Fe(CO)4(pz)], respectively. Herein we describe how the true nature of these solutions can be better explained by a valence‐disproportionation reaction of the diiron nonacarbonyl, induced by the donor solvent THF, resulting in the compound [Fe(THF)6][Fe3(CO)11]. The formation of the undecacarbonyl‐triferrate(2–) in such solutions was unambiguously confirmed by IR spectroscopy and by the isolation and crystallization of the corresponding salt (PPN)2[Fe3(CO)11]; its molecular structure was determined, however, already described in the literature.