POLARIZATION TRANSFER BETWEEN HETERONUCLEI - APPLICATION OF P-31, N-15-POLARIZATION TRANSFER TECHNIQUES IN N-15-NMR SPECTROSCOPY OF PHOSPHORUS-NITROGEN COMPOUNDS

A systematic study of sensitivity enhancement in N-15 NMR spectra of phosphorus-nitrogen compounds by P-31, N-15 polarisation transfer was performed using tris-(dimethylamino)phosphine (1) as a model compound. The application of several multipulse techniques (refocussed and non-refocussed INEPT, DEPT) and decoupling schemes shows that maximum enhancement was reached with the non-refocussed INEPT sequence, whereas the performance of longer pulse sequences was deteriorated by relaxation effects. The practical application of the technique was demonstrated for the determination of N-15 data of low coordinate phosphorus-nitrogen compounds (iminophosphines and imidometaphosphate ions). In favourable cases, the sensitivity gain may be comparable to that of H-1, N-15 INEPT measurements via long-range couplings. In addition to the 1D experiments, the practicability of heteronuclear correlation spectroscopy was demonstrated by the measurement of 2D P-31, N-15 shift-correlated spectra of 1.