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 (JPF) 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.