Unsymmetrically substituted N-heterocyclic phosphenium ions

Reduction of an unsymmetrically substituted α-diimine followed by condensation with PCl3 yielded a P-chloro-N-aryl-N′-alkyl diazaphospholene which was further converted into an unsymmetrical diazaphospholium triflate by reaction with trimethylsilyl triflate. Reaction of tetramers of N-H- or N-alkyl-benzo-1,3,2-diazaphospholes with methyl triflate or triflic acid led in one step to triflate salts of unsymmetrically substituted benzo-1,3,2-diazaphospholium cations. Determination of the crystal structures of two of these derivatives by single-crystal X-ray diffraction studies revealed that individual cations and anions in the crystal lattice interact via specific electrostatic, π-stacking, or van-der-Waals type interactions to form supramolecular assemblies. Thermoanalytical measurements disclosed that benzo-diazaphospholium triflates with medium length alkyl chains melt below 100 °C and exhibit a strong tendency to form supercooled liquids.