Cyclic Arsenic-Nitrogen Cations

A series of different cyclo-diarsa-diazenium salts bearing several bulky groups such as supermesityl (Mes* = 2,4,6-tBu(3)C(6)H(2)) 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 pi 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-mu-azido-hexachlorido-digallate. The Cl-/N-3(-) exchange is triggered by the action of the Lewis acid GaCl3. Depending on the Me3SiN3 stoichiometry, different mu-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 A in cyclo-diarsadiazenium salts of the type [R2N2As2Y]X-+(-) depending on the bulky group R (R = Mes*, Ter), the substituent Y (Y=Cl, N-3, OTf), and the anion X- (X = OTf, GaCl4, Cl3Ga-N-3-GaCl3), was established.