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 View the MathML source2-R3′E (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 N–BH3 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 N–R 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 N–BH3 adducts of 2-lithium-5-methyl-[1,3,5]-dithiazinanes of anchored conformation proceed with retention of C2 configuration.