3H-1,2,3,4-Triazaphosphole Constructs Derived from Sterically Encumbered Aryl Polyazides: Synthesis, Structure, and Reactivity

Abstract

Starting from sterically hindered aniline derivatives containing one or more Ar–NH₂ moieties, a series of aryl-azides have been synthesized. The reactions of these mono-, di-, and triaryl azides, ArN₃, (ArN₃)₂, and (ArN₃)₃ with phosphaalkynes R–C≡P (R = adamantyl or 2,4,6-tri-t-butylphenyl) yielded mono-, bis-, and tris-triazaphosphole assemblies. All the products are formed under ambient conditions under prolonged stirring. Representative triazaphospholes can be selectively alkylated with Meerwein’s reagent on the most nucleophilic nitrogen atom to yield stable 1,2,3,4-triazaphospholenium cations. These compounds were characterized by multinuclear NMR spectroscopy (¹H, ¹³C, ³¹P, ¹⁹F, and ¹¹B), mass spectrometry, and photophysical studies. Molecular structures of representative compounds have also been determined by single crystal X-ray diffraction. Additional density functional theory (DFT), TD-DFT, and NICS calculations were performed and the result were found to be in agreement with our experimental findings.