Synthesis and oxidation of phosphine cations†
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.