Structural analyses of 2-triorganylsilyl- and 2-triorganylstannyl derivatives of 5-alkyl-[1, 3, 5]-dithiazinanes. Do S⋯Si and S⋯Sn interactions exist?

A series of 2 - R′₃E (E = Si or Sn; R′ = Me or Ph) derivatives of 5-R-[1, 3, 5]-dithiazinanes (R = Me, iPr, tBu) are reported, as well as some of their NeBH³ adducts. Structures were determined by ²⁹Si, ¹¹⁹Sn, ¹¹B, ¹³C and ¹H NMR and X ray diffraction analyses. Minimum energy conformations were calculated by HF/6- 31++G(d, p) and B3LYP/6-31++G(d, p) methods. Preferred conformations and steric and stereoelectronic interactions are analyzed. In the solid state the ring conformation is a chair with the NeR group in axial and the 2-substituents in equatorial position. The Si or Sn atoms linked to C-2 have short distances to the two sulfur atoms, interpreted as Si⋯S and Sn⋯S stabilizing contacts. The ¹¹⁹Sn NMR chemical shifts and ¹J(¹³C, ¹¹⁹Sn) coupling constants evidenced weak S⋯Sn coordination bonds. Substitution reactions at C2 performed in NeBH³ adducts of 2-lithium-5-methyl-[1, 3, 5]-dithiazinanes of anchored conformation proceed with retention of C2 configuration.