Covalent alternatives for the elusive iminophosphonium cation. Crystal structures of PCl(NPri2)2NPh·AlCl3 and P(NPri2)2[NPh(SO2CF3)]O

Abstract

Reactions between diaminoiminophosphinic chlorides and the chloride-abstracting agents AlCl₃ and Ag(SO₃CF₃) have been comprehensively examined as potential routes to the three-co-ordinate iminophosphonium cation. However, bis(dialkylamino)(phenylimino)phosphinic chlorides react to give the covalent phosphoryl systems PCl(NR₂)₂NPh·AlCl₃ and P(NR₂)₂[NPh(SO₂CF₃)]O respectively, in quantitative yield. The AlCl₃ complexes are also prepared quantitatively from the reaction of P(NPrⁱ₂)₂⁺AlCl₄^– with PhN₃(Staudinger reaction). All compounds have been comprehensively characterised and the structures of the isopropyl derivatives confirmed by X-ray crystallography. Crystal data: PCl(NPrⁱ₂)₂NPH·AlCl₃, space group P2₁, a= 8.719(2), b= 15.553(2), c= 9.509(2)Å, β= 102.73(2)°, Z= 2, R= 0.029; P(NPrⁱ₂)₂[NPh(SO₂CF₃)]O, space group P2₁/n, a= 10.594(3), b= 13.222(2), c= 17.084(3)Å, β= 97.71(2)°, Z= 4, R= 0.048. The results indicate that the three-co-ordinate diaminoiminophosphonium cation is thermodynamically unstable with respect to the observed alternative covalent structures, and that steric shielding is responsible for the stability of the analogous diaminomethylenephosphonium cation.