1H-1,2,4-diazaphospholes: Synthesis, structural characterization, and DFT calculation

A few 1H-1,2,4-diazaphospholes H[3,5-R2dp] (R = methyl (5a), p-tolyl (5b), 1-naphthyl (5c), 2-furanyl (5d), 2-thienyl (5e), and isopropyl (5f)) were prepared and structurally characterized by a substantial experimental modification of the synthetic protocol. The molecules of all compounds are linked into oligomers via the bridges of NH⋯N hydrogen bonds in solid state. The tetrameric feature of 5a, and 5d–f represents a new motif of hydrogen-bonded 1H-1,2,4-diazaphospholes in solid state. The DFT calculation at the B3LYP/6-311++G** level suggested the possible proton disorder with intermolecular solid state proton transfer (ISSPT) between 1H-1,2,4-diazaphosphole rings.