The relative stabilities of PhE(NH-t-Bu)2 and PhE(μ-N-t-Bu)2EPh (E = As, Sb, and Bi):: X-ray structures of {Li2[PhAs(N-t-Bu)2]}2 and PhE(μ-N-t-Bu)2EPh (E = Sb, Bi)

The reaction of PhECl2 with 2 equiv of LiHN-t-Bu has been studied for the series E = As, Sb, and Bi to determine the effect of the phenyl group on subsequent amine condensation processes. For PhAsCl2, the metathesis product PhAs(NH-t-Bu)(2) 4 was obtained as a colourless oil. Similar reactions involving PhECl2, where E = Sb or Bi, yielded the cyclodipnict(III)azanes PhE(mu-N-t-Bu)(2)EPh 5 (E = Sb) and 6 (E = Bi), respectively. Treatment of 4 with 2 equiv of n-BuLi produced the dilithium salt Li-2[PhAs(N-t-Bu)(2)] 7a. Products 4, 5, 6, and 7a were characterized by H-1, Li-7 (7a), and C-13 NMR spectra, while 5, 6, and 7a were also structurally characterized by X-ray crystallography. Compound 7a is dimeric in the solid state via intermolecular Li...N and eta(6)-Li...Ph interactions. The cyclodipnict(III)azanes 5 and 6 have similar structures, with the exocyclic phenyl groups in trans positions relative to the E2N2 ring. This synthetic approach provides a new route to the four-membered rings RE(mu-N-t-Bu)(2)ER (E = Sb, Bi) and the first example of a bis(organyl)cyclodibism(III)azane.