NMR and theoretical analyses of electronic effects in N-BH3 adducts of (1,3,5-dithiazin-2-yl)silanes and stannanes. Intramolecular interactions of chemically identical S···S atoms

Abstract

The electronic effects produced by BH3 coordination to SiMe2Dtz2, SiMeDtz3, SiPhDtz3, SnMeDtz3 and SnPhDtz3 (Dtz = 5-methyl-1,3,5-dithiazinan-2-yl group) have been studied by 1H, 13C, 11B, 29Si and 119Sn NMR spectroscopy. It has been found that these effects are transmitted until seven bonds away. The X-ray diffraction analyses of SiMe2Dtz2 and its diborane adduct SiMe2(DtzBH3)2 showed for the latter an unexpected, folded conformation that facilitates intramolecular chemically identical sulphur-sulphur interactions. The existence of S···S, S···Si and S···Sn stabilising weak interactions was confirmed by ab-initio calculations, especially by the reduced gradient and the electrostatic potential of the electronic density maps. The electronic withdrawal effect of the N→BH3 groups drastically modifies the NBO charges of the sulphur atoms and their intramolecular interactions. It has concluded that the sulphur lone pairs interactions through-the-space explain the molecules conformation and the long-distance electronic effects.