SOLID-STATE P-31 NMR INVESTIGATIONS OF UNSATURATED PHOSPHORUS NITROGEN SULFUR RINGS

Solid-state CP/MAS P-31 NMR spectra were measured for the following unsaturated phosphorus-nitrogen-sulfur ring systems: 1,5-R4P2N4S2 (R = Me, Et, Ph), 1,5-Ph4P2N4S2Ph2, Ph2PN4S3NPPH3 and Ph2PN3S2. The isotropic solid-state shifts correlate well with the corresponding shifts in solution, the largest difference being 9.0 ppm, indicating that there are no phase-dependent structural features. Analysis of the principal elements of the shielding tensor by the spinning side band method showed that one of these elements is primarily responsible for the anomalously low-field isotropic chemical shifts of 1,5-R4P2N4S2, but no correlation was found between this individual tensor component and any of the structural parameters of these folded eight-membered rings. Two isotropic shifts were observed for the crystallographically inequivalent phosphorus atoms of 1,5-Et4P2N4S2, but the individual P-31 isotropic shifts of 1,5-Me4P2N4S2 were not resolved.