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

In the literature it was proposed that the treatment of [Fe 2 (CO) 9 ] in THF resulted, during dissolution, in deep red solutions which should presumably contain labile complexes “Fe(CO) 4 THF”. 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 ][Fe 3 (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 [Fe 3 (CO) 11 ]; its molecular structure was determined, however, already described in the literature.