Solid-state NMR studies of fluorinated diazadiphosphetidines

Abstract

A solid-state NMR study of three diazadiphosphetidines with fluorine substituents has been carried out in order to obtain information on structural and dynamic properties. The ¹⁹F and ³¹P spectra are discussed in relation to X-ray results. The NMR data depend on the substituents at both the phosphorus and nitrogen positions, and motional properties observed in solution-state NMR are slowed in the solid state, but can still be investigated. Axial and equatorial fluorine positions have been distinguished by (fluorine) chemical shift, effective shielding anisotropies and isotropic (J_PF) coupling for (PhF₂PNMe)₂ at ambient probe temperature. Axial ⇆ equatorial exchange is also shown to be slowed on the NMR timescale for (F₃PNPh)₂ at low temperature. Analysis of spinning sideband manifolds has yielded data on effective shielding anisotropies for both ³¹P and ¹⁹F spectra. Triple resonance ³¹P-{¹⁹F, ¹H} experiments have allowed the determination of true shielding tensor parameters. For (Ph₂FPNMe)₂ a triple-fit procedure has provided additional data, though not to high accuracy. Static ¹⁹F and ³¹P spectra, MAS ¹³C and ¹⁵N spectra and some relaxation times are also reported and discussed.