Cyclic Arsenic−Nitrogen Cations

Abstract

A series of different cyclo-diarsa-diazenium salts bearing several bulky groups such as supermesityl (Mes* = 2,4,6-tBu₃C₆H₂) and m-terphenyl (2,6-Mes₂-C₆H₃, Mes = 2,4,6-Me₃C₆H₂) and anions such as triflate (OTf = SO₃CF₃ = trifluoromethylsulfonate) and tetrachloridogallate (GaCl₄⁻) were synthesized and fully characterized. The novel 1-chloro-cyclo-1,3-diarsa-2,4-diazenium cation represents the first example of a binary cyclic As(III)/N four-membered heterocyclic cation, with a di- and tricoordinated As atom and a delocalized π bond along the NAs⁽⁺⁾N unit. The addition of excess Me₃SiN₃ yields the fully characterized cationic arsenic azide, 1-azido-cyclo-1,3-diarsa-2,4-diazenium-μ-azido-hexachlorido-digallate. The Cl⁻/N₃⁻ exchange is triggered by the action of the Lewis acid GaCl₃. Depending on the Me₃SiN₃ stoichiometry, different μ-azido-hexachlorido-digallate salts with either 1-chloro- or 1-azido-cyclo-1,3-diarsa-2,4-diazenium cations or even a mixture of both are observed. Moreover, it was of special interest to study the distances between the cationic arsenic center and the anion in cyclo-diarsa-diazenium salts. A correlation between the color of the salt and the anion/cation distance, ranging between 2 and 8 Å in cyclo-diarsa-diazenium salts of the type [R₂N₂As₂Y]⁺X⁻ depending on the bulky group R (R = Mes*, Ter), the substituent Y (Y = Cl, N₃, OTf), and the anion X⁻ (X = OTf, GaCl₄, Cl₃Ga−N₃−GaCl₃), was established.