HEXACOORDINATE PHOSPHONIUM SALTS INCORPORATING 2 (8-DIMETHYLAMINO)-1-NAPHTHYL LIGANDS - STRUCTURE AND REACTIVITY

New hexacoordinate phosphonium salts Ar(2)RZP(+) X-[Ar = (8-dimethylam ino)-1-naphthyl] with two N-->P intramolecular coordinations are descr ibed. NMR studies of these salts and the X-ray structure of one of the m, 5 (R = Ph, Z = H, X = Br) show that they have a dissymmetric struct ure with the two Me2N groups coordinated at the phosphorus centre. Sal ts 4 (R = Ph or Me, Z = CH2CO2Et) react slowly with PhCHO under Wittig conditions probably because of the steric hindrance around the phosph orus atom. This is confirmed by the higher reactivity of the less hind ered pentacoordinate phosphonium salts ArR2P+CH2CO2Et X- 11 (R = Ph or Me) which are also much more reactive than Ph3P+CH2CO2Et Br-. This st udy points out the increase of reactivity of these salts due to the N- ->P interaction.