Conformations of diphosphinoamines; variable-temperature nuclear magnetic resonance and X-ray crystallographic studies

Abstract

The variable-temperature ³¹P-{¹H} n.m.r. spectra of a series of diphosphinoamines, X₂PN(R)PX₂(R = H, Me, Et, or Prⁱ, X = Ph; R = Me, Bu^t, or CH₂Bu^t, X = Cl; R = Me or Bu^t, X = F; R = Et, X = NMe₂) have been studied. Complementary information on these compounds has been obtained from ¹H, ¹³C, and ¹⁹F n.m.r., including double and triple resonance experiments. The coupling constant, ²J(PNP), covers the range –23.9 to 731.9 Hz, and its magnitude and sign can be related to the proportion of molecules in which the local symmetry of the P–N–P skeleton is C_2v rather than C_S. Diphosphinoamine conformers of the latter type have been clearly identified for the first time both in solution (for R = Et or Prⁱ, X = Ph, and R = Bu^t or CH₂Bu^t, X = Cl) and also in the solid phase. X-Ray analysis of Ph₂PN(Prⁱ)PPh₂, based on 1 269 diffractometric intensities refined to R= 0.035, shows that the symmetry of the P–N–P skeleton is close to C_s in the solid, with P–N = 1.706(4) and 1.711(4)Å, and PNP = 122.8(3)°.