Bis(ylide)-substituted phosphenium and phosphonium halides

The bis(triphenylphosphoniumyldyl)halophosphines expected from the condensation of ylidyl dihalophosphines with trimethylsilyl ylides or of their addition to carbodiphosphoranes enter a spontaneous dissociation to yield bis(ylidyl)phosphenium halides. They are the first phosphenium salts which do not need anions of low basicity such as AlCl4-. P-31 NMR spectra and, in one case, a single-crystal X-ray investigation reveal an essentially planar structure of the PCPCP skeleton with E,E-conformation. The bis(ylidyl)phosphenium halides are protonated at an ylidic carbon atom while at the same time the halide ion is re-associated to the central phosphorus atom. They add halogen or ortho quinones to the central phosphorus to yield the corresponding phosphonium ions. They are also oxidized by elemental sulfur or gray selenium resulting in bis(ylidyl)thio- and -seleno-phosphinyl halides. As can be shown by their solvent dependent P-31 NMR spectra, they dissociate in polar media to yield the first examples of chalcogenoxophosphonium halides. As revealed by another X-ray structure analysis, the conjugation in a bis(ylidyl)dihalophosphonium ion is interrupted at the central phosphorus atom.