Synthesis, crystal structures and spectroscopic properties of cationic carbyne complexes of molybdenum and tungsten supported by tripodal nitrogen, phosphorus and sulphur donor ligands

Reaction of the tridentate ligands HCpy₃ or Ppy₃ (py = 2-pyridyl) with Cl(CO)₂py₂M=CPh (M = Mo, W) in THF at elevated temperature followed by metathesis with NaBPh₄ in CH₃CN affords [(n³-Xpy₃)(CO)₂M=CPh]⁺ (M = W, X = P (2), HC (3); M = Mo, X = P (4)) in high yield. Interaction between 1,1,1-tris(diphenylphosphinomethyl)ethane (CH₃C(CH₂PPh₂)₃) or 1,4,7-trithiacyclononane (TTCN) and Cl(CO)₂py₂W≡CPh in the presence of AgPF₆ in refluxing CH₃CN gives [{CH₃C(CH₂PPh₂)₃}(CO) ₂W=CPh]PF₆ (5) and [(TTCN)(CO)₂W≡CPh]PF₆ (6), respectively. These complexes exhibit intense absorption bands at 320-340 nm and weak absorptions in the 400-500 nm region, while excitation at 330 nm in dichloromethane give intense orange to red emission. The structure of the product (1) from reaction of Ppy₃ with Cl(CO)₂py₂W=CPh was established by X-ray crystallography and shows that only two of the pyridine rings in Ppy₃ are bound to the metal center. The crystal structures of 2 · EtOH and 3 · EtOH show that the W-N distance trans to the carbyne moiety is significantly longer than those which are cis, and this is attributed to the strong trans influence of CPh compared to CO.