The bis(alkynyl) derivatives [Fe(CCR)₂L₄][R = Ph, p-tolyl or Bu^t; L = P(OMe)₃, P(OEt)₃ or PPh(OEt)₂] were prepared and their protonation and methylation reactions with HBF₄ and CF₃SO₃Me afforded alkynyl–vinylidene cations [Fe(CCR){CC(H)R}L₄]⁺ and [Fe(CCR){CC(Me)R}L₄]⁺, respectively. The aryldiazovinylidene [Fe(CCR){CC(NNC₆H₄Me-p)Ph}{P(OEt)₃}₄]BPh₄ was also prepared. The complexes were characterized by infrared and ¹H, ³¹P and ¹³C NMR spectra and the crystal structure of [Fe(CCPh){CC(H)Ph}{P(OEt)₃}₄]BF₄ has been determined. The reactivity of the new vinylidene complexes was studied and showed the rearrangement in solution of the [Fe(CCR){CC(H)R}L₄]⁺ cations to enynyl [Fe(η³-RC₃CHR)L₄]⁺ derivatives only in the case of LPPh(OEt)₂. Deprotonation with base giving [Fe(CCR)₂L₄] as well as substitution of the vinylidene ligand in [Fe(CCR){CC(H)R}L₄]⁺ cations by CO and CNC₆H₄Me-p giving [Fe(CCR)-(CO){P(OEt)₃}₄]⁺ and [Fe(CCR)(p-MeC₆H₄NC){P(OEt)₃}₄]⁺ derivatives are also discussed.