HEXACOORDINATE PHOSPHONIUM SALTS InCORPORATING TWO (8-DIMETHYLAMINO)-1-NAPHTHYL LIGANDS. STRUCTURE AND REACTIVITY

New hexacoordinate phosphonium salts Ar2RZP+ X-[ar=(8-dimethylamino)-1-naphthyl] with two N→P intramolecular coordinations are described. NMR studies of these salts and the X-ray structure of one of them, 5 (R=Ph, Z=H, X=Br) show that they have a dissymmetric structure with the two Me2N groups coordinated at the phosphorus centre. Salts 4 (R=Ph or Me, Z=CH2CO2Et) react slowly with PhCHO under Wittig conditions probably because of the steric hindrance around the phosphorus atom. This is confirmed by the higher reactivity of the less hindered pentacoordinate phosphonium salts ArR2PCCH2C02Et X− 11 (R=Ph or Me) which are also much more reactive than Ph3P+CH2CO2Et Br−. This study points out the increase of reactivity of these salts due to the N→P interaction.