Reactivity studies of an imine-functionalised phosphaalkene; unusual electrostatic and supramolecular stabilisation of a σ<sup>2</sup>λ<sup>3</sup>-phosphorus motif <i>via</i> hydrogen bonding
periphery forms protonated adducts displaying hydrogenbonding interactions. These materials are significantly more stable than the parent species, demonstrating an unprecedented approach towards the stabilisation of a multiple-bonded heavy main group fragment, in this case, a phosphaalkene. An HCl adduct self-assembles with H2O into a dimeric network displaying a discrete quadrilateral hydrogen-bonded