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)

Article abstract of DOI:10.1139/v03-019

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(μ-N-t-Bu)₂EPh 5 (E = Sb) and 6 (E = Bi), respectively. Treatment of 4 with 2 equiv of n-BuLi produced the dilithium salt Li₂[PhAs(N-t-Bu)₂] 7a. Products 4, 5, 6, and 7a were characterized by ¹H, ⁷Li (7a), and ¹³C 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 η⁶-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(μ-N-t-Bu)₂ER (E = Sb, Bi) and the first example of a bis(organyl)cyclodibism(III)azane.