Arsenosiloxane: Bildung und Zerfall von Trialkylsilyl‐arsenaten und ‐arseniten

Arsenosiloxanes: Formation and Decomposition of Trialkylsilyl Arsenates and Arsenites Tris(trialkylsilyl) arsenates(V) are prepared from silver arsenate(V) and chlorotrialkylsilanes or from arsenic acid and hexaalkyldisilazanes. The triethylsilyl ester 1b is stable, but the trimethylsilyl ester 1a undergoes condensation at ambient temperature to give hexamethyldisiloxane and trimethylsilylpolyarsenates(V), including tetrakis(trimethylsilyl) diarsenate(V) (4a). According to an X‐ray crystal structure determination of 4a (triclinic, space group P1) centrosymmetrical dimers are present containing two edge‐sharing AsO₆ octahedra with apex‐bridging by two AsO₄ tetrahedra. 1a is converted into the salt [(Me₃SiO)₄As]⁺ CF₃SO₃⁻ the cation of which is believed to be a component of the reaction chain. There is also evidence by mass spectrometry for the existence of (Me₃SiO)₅As (5). — Tris(trimethylsilyl) arsenite(III) (6) is prepared from AsCl₃ and NaOSiMe₃. With modified stoichiometry, side reactions give also the byproducts Cl₂AsOSiMe₃, ClAs(OSiMe₃)₂, Cl₂AsOAsCl₂, Cl₂AsOAsCl(OSiMe₃), O[AsCl(OSiMe₃)]₂, and cyclic chloroarsenosiloxanes (12, 13).