Hexacoordinate phosphonium salts incorporating two (8-dimethylamino)-1-naphthyl ligands. Structure and reactivity

Article abstract of DOI:10.1080/10426509708044208

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 ArR₂P⁺CH₂CO₂Et 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.