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, L 2 = 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)(PMe 3)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]. © 2011 American Chemical Society.