Chemical Shift Tensors of Directly Bonded Phosphorus Nuclei in Unsaturated Four-Membered Rings. Solid-State 31P NMR and Theoretical Study of Trans- and Cis-Substituted Diphosphetes

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 1999-02, Vol.103 (8), p.1029-1037
• Main Authors: Bernard, Guy M, Wu, Gang, Lumsden, Michael D, Wasylishen, Roderick E, Maigrot, Nicole, Charrier, Claude, Mathey, François
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp984116h

The chemical shift (CS) tensors of two four-membered heterocyclic diphosphetes, trans- and cis-1,2-dihydro-1-methyl-2-phenyl-3,4-bis(tert-butyl)-1,2-diphosphete, have been investigated by solid-state 31P NMR spectroscopy. The dipolar chemical shift method has been employed to determine the magnitudes of the principal components of the 31P CS tensors in these compounds, as well as their orientations relative to the 31P−31P dipolar vector. The spans of the phenyl- and methyl-substituted phosphorus CS tensors of the trans isomer are 248 and 280 ppm, respectively, significantly larger than the corresponding values for the cis isomer, 139 and 173 ppm. The orientations of the CS tensors in the molecular framework are proposed on the basis of ab initio calculations using the gauge-independent atomic orbitals method. The combined experimental−theoretical results suggest that, for both the trans and cis isomers, the least shielded principal components, δ11, are oriented in the plane defined by the four-membered ring. For the trans isomer, the most shielded principal components, δ33, are approximately perpendicular to this plane; however, for the cis isomer, it is the δ22 components that are perpendicular to the plane of the four-membered ring. The spectra of magic-angle spinning samples of the trans isomer exhibit asymmetric, spinning-frequency dependent line shapes, while those of the cis isomer are invariant to spinning frequency. These observations are consistent with the CS tensors derived from the 31P NMR spectra of stationary samples.