The structure and fluxionality of [Fe-3(CO)(10)(dppe)]; a merry-go-round with no sense of direction

The crystal structure of [Fe-3(CO)(10)(dppe)] has been determined. The Ph2P CH2CH2PPh2 ligand bridges the Fe(mu-CO)(2)Fe edge and is markedly non-plana r. The non-planarity inverts with Delta G(211)(double dagger) = 48.4 +/- 0. 5 kJ mol(-1). The carbonyls on the bridged iron atoms exchange with the axi al ones by the merry-go-round mechanism with Delta G(195)(double dagger) = 43.4 +/- 0.5 kJ mol(-1). Despite the non-planar dppe ligand producing a chi ral molecule, the merry-go-round exchange goes with equal rate in both dire ctions. This is the first example of a six-toothed failed ratchet. (C) 2000 Elsevier Science S.A. All rights reserved.