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 C6H4-4-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′].