Synthesis and oxidation of phosphine cations

Abstract

Cationic phosphines of the form [(L)PPh₂]⁺ are prepared by reaction of Ph₂PCl with carbenes (L) including a chiral bis(oxazoline)-based carbene, a cyclic(alkyl)(amino) carbene (cAAC), and a 1,2,3-triazolium-derived carbene, affording the products, [(IBox-iPr₂)PPh₂][OSO₂CF₃] 1, [(cAAC)PPh₂][OSO₂CF₃] 2 and [((TripCH₂N₂(NMe)C₂Ph)PPh₂)₂(AgCl)₂][Cl]₂3. Using PhPCl₂, the related dication [CH₂(NC₃H₂NDipp)₂PPh]²⁺4 was also prepared. Crystallographically-determined metric parameters and computational data indicate that these species are best described as cationic phosphines rather than phosphenium cations. The oxidation of these cations with XeF₂ afforded [(IBox-iPr₂)PF₂Ph₂][OSO₂CF₃] 5, [(cAAC)PF₂Ph₂][OSO₂CF₃] 6 and [(TripCH₂N₂(NMe)C₂Ph)PF₂Ph₂][Cl] 7; 4 was not oxidized. These observations are understood by a computational assessment of the average local ionisation potentials at valence shell charge concentrations identified via topological analysis of the electron density.