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The synthesis of the iron allenylidene complexes [(g 5 -C 5 Me 5 )(g 2 -dppe)Fe(=C=C=C(Ph)Ph)][X] (5a, X = PF 6 , 95%; 5b, X = BPh 4 , 91%; dppe = 1,2-bis(diphenylphosphino)ethane) was achieved by reacting the complex (g 5 -C 5 Me 5 )(g 2 -dppe)FeCl (10) with 1 equiv of 1,1-diphenyl-prop-2-yn-1-ol in methanol in the presence of KPF 6 or NaBPh 4 . Surprisingly, when the reaction was carried out in the presence of the tetraphenylborate anion, the final product contained both 5b and the hydroxyvinylidene [(g 5 -C 5 Me 5 )(g 2 -dppe)Fe(=C=C(H)C(OH)(Ph) 2 )][BPh 4 ] (14b) in the 1:1 ratio. Further treatment of the mixture with Amberlyst 15 in methanol provided the allenylidene 5b as a pure sample. The allenylidene complexes [(g 5 -C 5 Me 5 )(g 2dppe)Fe(=C=C=C(Me)Ph)][PF 6 ] (6) and [(g 5 -C 5 Me 5 )(g 2 -dppe)Fe(=C=C=C(Me)Et)][PF 6 ] (7) were prepared according to the same procedure and they were isolated as purple powders in 90% yield. The X-ray crystal structures were determined for the vinylidene complexes [(g 5 -C 5 Me 5 )(g 2 -dppe)Fe(=C=CH 2 )][PF 6 ] (3) and [(g 5 -C 5 Me 5 )(g 2 -dppe)Fe(=C=C(Ph)H)][PF 6 ] (4), and the allenylidene derivative 5a. In the homogeneous series of complexes [(g 5 -C 5 Me 5 )(g 2 -dppe)Fe(=(C) n (R)R')][

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