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′].

本研究合成并完成结构表征了两类双膦取代环戊二烯基钼炔基配合物（bis-phosphine-substituted cyclopentadienyl molybdenum alkynyl complexes），即[Mo(C≡CR)(CO)(dppe)Cp′]与反式（trans）-[Mo(C≡CR)(CO)(三甲基膦（PMe₃ / Trimethylphosphine）)₂Cp′]。其中R为苯基（Ph / Phenyl）或4-甲基苯基（C₆H₄-4-Me / 4-Methylphenyl）；dppe为1,2-双(二苯基膦)乙烷（1,2-Bis(diphenylphosphino)ethane，即Ph₂PCH₂CH₂PPh₂）；Cp′为环戊二烯基（Cp / Cyclopentadienyl）或五甲基环戊二烯基（Cp* / Pentamethylcyclopentadienyl）。研究团队通过循环伏安法（cyclic voltammetry）对这两类配合物经单电子氧化生成17电子自由基阳离子的过程展开了探究；针对部分Cp*衍生物，还采用了光谱电化学红外（spectroelectrochemical IR）与紫外-可见光谱法（UV–visible spectroscopy）开展表征测试。结合红外（IR）、电子顺磁共振波谱（EPR spectroscopy / Electron Paramagnetic Resonance spectroscopy）实验测试与基于密度泛函理论（DFT / Density Functional Theory）的计算分析，本研究明确了两类配合物[Mo(C≡CR)(CO)(dppe)Cp′]与反式-[Mo(C≡CR)(CO)(PMe₃)₂Cp′]之间存在的多项显著差异。具体而言，相较于反式-[Mo(C≡CR)(CO)(PMe₃)₂Cp′]以金属为中心（metal-centered）的最高占据分子轨道（HOMO / Highest Occupied Molecular Orbital），[Mo(C≡CR)(CO)(dppe)Cp′]的HOMO中炔基轨道特征得到了显著增强，这一变化源于分子几何构型的改变。