The structure and fluxionality of [Fe3(CO)10(dppe)]; a merry-go-round with no sense of direction

The crystal structure of [Fe3(CO)10(dppe)] has been determined. The Ph2PCH2CH2PPh2 ligand bridges the Fe(μ-CO)2Fe edge and is markedly non-planar. The non-planarity inverts with ΔG‡211=48.4±0.5 kJ mol−1. The carbonyls on the bridged iron atoms exchange with the axial ones by the merry-go-round mechanism with ΔG‡195=43.4±0.5 kJ mol−1. Despite the non-planar dppe ligand producing a chiral molecule, the merry-go-round exchange goes with equal rate in both directions. This is the first example of a six-toothed failed ratchet.