A Highly Reactive Geminal P/B Frustrated Lewis Pair: Expanding the Scope to C-X (X=Cl, Br) Bond Activation

The geminal frustrated Lewis pair tBu₂ PCH₂ B(Fxyl)₂ (1; Fxyl=3,5-(CF₃ )₂ C₆ H₃ ) is accessible in 65 % yield from tBu₂ PCH₂ Li and (Fxyl)₂ BF. According to NMR spectroscopy and X-ray crystallography, 1 is monomeric both in solution and in the solid state. The intramolecular P⋅⋅⋅B distance of 2.900(5) Å and the full planarity of the borane site exclude any significant P/B interaction. Compound 1 readily activates a broad variety of substrates including H₂ , EtMe₂ SiH, CO₂ /CS₂ , Ph₂ CO, and H₃ CCN. Terminal alkynes react with heterolysis of the C-H bond. Haloboranes give cyclic adducts with strong P-BX₃ and weak R₃ B-X bonds. Unprecedented transformations leading to zwitterionic XP/BCX₃ adducts occur on treatment of 1 with CCl₄ or CBr₄ in Et₂ O. In less polar solvents (C₆ H₆ , n-pentane), XP/BCX₃ adduct formation is accompanied by the generation of significant amounts of XP/BX adducts. FLP 1 catalyzes the hydrogenation of PhCH=NtBu and the hydrosilylation of Ph₂ CO with EtMe₂ SiH.