cis-Cyclodiphosph(v/v)azanes as highly stable and robust main group supramolecular building blocks

Abstract

Cyclophosphazanes have been extensively studied over the past decades due to their topological flexibility and unique chemical versatility. However, their use in supramolecular chemistry and crystal engineering is still in its infancy. Here, we report the synthesis of cis-Se-oxidized cyclodiphosph(V/V)azane 1 as a model cyclophosphazane compound and its use as supramolecular building blocks. The displayed cis-conformation, along with its tendency to adopt an exo, exo configuration of the terminal tert-butylamino substituents, enables the formation of highly reproducible supramolecular synthons via R²₁(8) bifurcated hydrogen bonds. Such bifurcated hydrogen bonds formed by the cyclodiphosphazane scaffold contain larger bite angles than those of their more well-known urea, thiourea and squaramide counterparts. We obtained five different solvate crystals as well as three different cocrystals that all contain similar hydrogen bonding motifs. In addition, we envisioned that the Se atoms in the oxidized cyclodiphosph(V/V)azane can act as halogen bond acceptors, and we were able to successfully obtain a cocrystal with 1,4-dibromo-tetrafluorobenzene, via the formation of PSe⋯Br halogen bonds. Such interaction had only been reported once before and warrants further exploration. Our results demonstrate the versatility and robustness of the cyclodiphosph(V/V)azane scaffold and highlights its potential as a prospective building block for creating reproducible supramolecular synthons for main group crystal engineering purposes.