Syntheses and Solid-State Structure Analyses of Pentafluoroethylated Arsanes

Herein, we report an improved synthesis of pentafluoroethylated arsanes. Deprotonation of pentafluoroethane by <i>n</i>-butyllithium yields the readily available pentafluoroethyllithium, which can be handled at low temperatures. Subsequent reaction with arsenic trichloride affords tris(pentafluoroethyl)arsane in good yields. Control of the degree of substitution at the arsenic center is achieved via the introduction of diethylamino protecting groups. The aminoarsanes AsCl₂(NEt₂) and AsCl(NEt₂)₂ react smoothly with LiC₂F₅, enabling the isolation of As(C₂F₅)₂(NEt₂) and As(C₂F₅)(NEt₂)₂. Cleavage of the diethylamino protecting group with gaseous HCl or HBr affords the corresponding halogenoarsanes. All products represent colorless, volatile liquids, which are characterized by multinuclear NMR spectroscopy. Crystallization of As(C₂F₅)₃ as well as As(C₂F₅)_<i>n</i>Cl_3-<i>n</i> and As(C₂F₅)_<i>n</i>Br_3-<i>n</i> (<i>n</i> = 1,2) is facilitated by <i>in situ</i> crystallization techniques, and the solid-state structures are subsequently determined by X-ray diffraction analysis.