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 1 b is stable, but the trimethylsilyl ester 1 a undergoes condensation at ambient temperature to give hexamethyldisiloxane and trimethylsilyl polyarsenates(V), including tetrakis(trimethylsilyl) diarsenate(V) (4a). According to an X-ray crystal structure determination of 4a (triclinic, space group P1BAR) centrosymmetrical dimers are present containing two edge-sharing AsO6 octahedra with apex-bridging by two AsO4 tetrahedra. 1 a 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).