BIS(YLIDE)-SUBSTITUTED PHOSPHENIUM AND PHOSPHONIUM HALIDES

The bis(triphenylphosphoniumyldyl)halophosphines expected from the con densation 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 phospheni um 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 re veal an essentially planar structure of the PCPCP skeleton with E,E-co nformation. The bis(ylidyl)phosphenium halides are protonated at an yl idic carbon atom while at the same time the halide ion is re-associate d to the central phosphorus atom. They add halogen or ortho quinones t o 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 me dia to yield the first examples of chalcogenoxophosphonium halides. As revealed by another X-ray structure analysis, the conjugation in a bi s(ylidyl)dihalophosphonium ion is interrupted at the central phosphoru s atom.