Solid-State NMR and X-ray Diffraction Studies of the Geometry and Intramolecular Dynamics of Bis(organothiophosphoryl) Dichalcogenides

Abstract

Information stored in the Cambridge Crystallographic Data Centre shows that anti−anti conformation is common for bis(organothiophosphoryl) dichalcogenides. In view of the 1−4 repulsion, the syn−syn conformation of the S1P−X−X4−PS (X = S and Se) backbone is unfavorable. However, in compounds with at least one phenyl group directly bonded to the phosphorus, such as bis[tert-butyl(phenyl)thiophosphinyl] disulfide (Knopik, P. et al. J. Chem. Soc., Dalton Trans. 1993, 2749), bis(diphenylthiophosphinyl) disulfide (Gallacher, A. C. et al. Acta Crystallogr. 1993, C49, 1793) and bis[tert-butyl(phenyl)thiophosphinyl] diselenide (this work) there is the syn−syn geometry caused by the aromatic−aromatic interactions. Bis[tert-butyl(phenyl)thiophosphinyl] diselenide is monoclinic, space group C2/c with a = 20.424(2) Å, b = 9.373(1) Å, c = 12.907(1) Å, V = 2406.4(2) Å3, Dc = 1.525 (2) g/cm3, and Z = 4. Refinement using 2351 reflections for 118 variables gives R = 0.047. We have used high-resolution 77Se MAS NMR to study the structural properties of the compound. The principal elements Tii of the 77Se effective dipolar/chemical shift tensor were calculated from the intensities of the spinning sidebands. The values of the anisotropy and asymmetry parameters reflect the distortion of the environment of selenium. For a series of bis(organothiophosphoryl) diselenides the T33 tensor component gives the largest contribution to the isotropic chemical shifts and the span parameter Ω reflects the strength of the diselenide bond. Molecular packing significantly influences the intramolecular dynamics of the aliphatic and aromatic groups. The 13C dipolar dephasing experiment and line shape analysis of the 1H−2H CP/MAS spectra of selectively 2H-labeled compounds show that the phenyl groups are static as a result of the aromatic−aromatic interaction, while the tert-butyl groups are under a fast motional regime, with C3v jumps around the P−C and C−C bonds.