Synthesis, redox chemistry, and electronic structure of the alkynyl cyclopentadienyl molybdenum complexes [Mo(C≡CR)(CO)(L₂)Cp']ⁿ⁺ (n = 0 or 1; R = Ph or C₆H ₄-4-Me, L₂ = Ph₂PCH₂CH₂PPh₂ or 2PMe₃, Cp' = Cp or Cp*)

Two series of bis-phosphine-substituted cyclopentadienyl molybdenum alkynyl complexes, [Mo(C≡CR)(CO)(dppe)Cp′] and trans-[Mo(C≡CR)(CO)(PMe3)2Cp′] (R = Ph or C6H4-4-Me, dppe = Ph2PCH2CH2PPh2, Cp′ = Cp or Cp*), have been prepared and structurally characterized. One-electron oxidation to the 17-electron radical cations has been investigated by cyclic voltammetry and, for selected Cp* derivatives, by spectroelectrochemical IR and UV–visible methods. Through a combination of experimental measurements (IR and EPR spectroscopy) and DFT-based calculations some important differences between the two series of complexes [Mo(C≡CR)(CO)(dppe)Cp′] and trans-[Mo(C≡CR)(CO)(PMe3)2Cp′] have been established. In particular, the change in molecular geometry leads to enhanced alkynyl character in the HOMO of [Mo(C≡CR)(CO)(dppe)Cp′] when compared with the largely metal-centered HOMO of trans-[Mo(C≡CR)(CO)(PMe3)2Cp′].