Preparation of trimeric and tetrameric bis(trifluoromethyl)arsazene; X-ray study of [(CF3)2AsN]4

Two new aminoarsines, (CF3)2AsN(SiMe3)2(1) and CF3As[N(SiMe3)2]2(2), are formed by reaction of (CF3)2AsCl and (CF3)AsCl2 with LiN(SiMe3)2. Chlorination of (1) yields [(CF3)2As(Cl)N(SiMe3)]2(3). On refluxing (3) in n-hexane or n-heptane, the synthesis of trimeric and tetrameric bis(trifluoromethyl)arsazenes, [(CF3)2AsN]3(4) and [(CF3)2AsN]4(5), is accomplished. Pyrolysis of (3) also produced (4) and (5). Crystals of (5) are triclinic, space group P, with a= 991.2(5), b= 1 012.9(6), c= 1 432.8(7) pm, α= 108.21(4), β= 96.03(4), γ= 109.44(4)°, and Z= 2. The structure was solved by direct methods and refined to R 0.069 for 2 183 unique observed diffractometer data. The molecular symmetry approximates to (S4), with a slight alternation in As–N distances [171.6(7) and 173.2(9) pm].