Cationic and Neutral Cp*M(NO)(κ²-Ph₂PCH₂CH₂PPh₂) Complexes of Molybdenum and Tungsten: Lewis-Acid-Induced...

Treatment of CH₂Cl₂ solutions of Cp*M(NO)Cl₂ (Cp* = η⁵-C₅(CH₃)₅; M = Mo, W) first with 2 equiv of AgSbF₆ in the presence of PhCN and then with 1 equiv of Ph₂PCH₂CH₂PPh₂ affords the yellow-orange salts [Cp*M(NO)(PhCN)(κ²-Ph₂PCH₂CH₂PPh₂)](SbF₆)₂ in good yields (M = Mo, W). Reduction of [Cp*M(NO)(PhCN)(κ²-Ph₂PCH₂CH₂PPh₂)](SbF₆)₂ with 2 equiv of Cp₂Co in C₆H₆ at 80 °C produces the corresponding 18e neutral compounds, Cp*M(NO)(κ²-Ph₂PCH₂CH₂PPh₂) which have been isolated as analytically pure orange-red solids. The addition of 1 equiv of the Lewis acid, Sc(OTf)₃, to solutions of Cp*M(NO)(κ²-Ph₂PCH₂CH₂PPh₂) at room temperature results in the immediate formation of thermally stable Cp*M(NO→Sc(OTf)₃)(H)(κ³-(C₆H₄)PhPCH₂CH₂PPh₂) complexes in which one of the phenyl substituents of the Ph₂PCH₂CH₂PPh₂ ligands has undergone intramolecular orthometalation. In a similar manner, addition of BF₃ produces the analogous Cp*M(NO→BF₃)(H)(κ³-(C₆H₄)PhPCH₂CH₂PPh₂) complexes. In contrast, B(C₆F₅)₃ forms the 1:1 Lewis acid-base adducts, Cp*M(NO→B(C₆F₅)₃)(κ²-Ph₂PCH₂CH₂PPh₂) in CH₂Cl₂ at room temperature. Upon warming to 80 °C, Cp*Mo(NO→B(C₆F₅)₃)(κ²-Ph₂PCH₂CH₂PPh₂) converts cleanly to the orthometalated product Cp*Mo(NO→B(C₆F₅)₃)(H)(κ³-(C₆H₄)PhPCH₂CH₂PPh₂), but Cp*W(NO→B(C₆F₅)₃)(κ²-Ph₂PCH₂CH₂PPh₂) generates a mixture of products whose identities remain to be ascertained. Attempts to extend this chemistry to include related Ph₂PCH₂PPh₂ compounds have had only limited success. All new complexes have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of most of them have been established by single-crystal X-ray crystallographic analyses.