Sixfold phenyl embraces with substituted phenyl in PPh3

Abstract

Examination of the Cambridge Structural Database reveals that Ph₄P⁺ cations and PPh₃ ligands in crystals associate through phenyl⋯phenyl non-bonded interactions which are attractive, concerted, and widespread. The strongest and most prevalent interaction is the energetically favourable sextuple phenyl embrace (6PE) in which there are six concerted edge-to-face (EF) phenyl–phenyl interactions. We have questioned the extent to which substitution on one or more phenyl rings would interfere with XPh₃ as a 6PE tecton. Substitution in the 4-position of Ph does not interfere with the formation of 6PEs. Substituents in other positions can be out of the interaction domain and not affect the 6PE, or if small like methyl they can form 6PE in which some of the EF motifs are replaced by methyl-to-face (MF). In some cases the substitution of Ph destroys the 6PE. Perfluorination, in (C₆F₅)₃PPtCl₂PtP(C₆F₅)₃, does not obstruct occurrence of chains of intermolecular 6PE. Hetero-molecular 6PE occur, and could be deployed for generation of acentric crystals. The cation (o-NH₂C₆H₄)Ph₃P⁺ can form chains of embraces analogous to the ZZI6PE, which is prevalent for Ph₄P⁺.