Synthesis of Novel Silicon-containing Multiple-bond Compounds by Taking Advantage of Steric Protection and Investigation of Their Structures and Reactivities

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1.The first stable silanethione Tbt(Tip)Si=S(1 : Tbt=2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Tip=2,4,6-triisopropylphenyl)was successfully synthesized by the desulfurization of the corres-ponding tetrathiasilolane, Tbt(Tip)SiS_4, with triphenylphoshine in hexane. Silanethione 1 was isolated as stable yellow crystals and it showed a characteristic downfield shifted signal at+166.6ppm(in C_6D_6)in the ^<29>Si NMR spectra suggesting the sp^2 character of the central silicon. The X-ray crystallographic structural analysis revealed that the Si-S bond length of 1 is ca. 9% shorter than that of the typical Si-Si single bond compounds and the silathiocarbonyl unit of 1 has a completely trigonal planar geometry as in the case of ketones. Silinethione 1 was found to have an enough space around the central siliconatom to react with small molecules, though the bulky substituents on Si atom of 1 effectively prevent its self-dimerization.2.The synthesis of a stable silaketeneimine, Tbt(Mes)Si=C … More =NAr, was also examined by the reaction of a sterically protected silylene Tbt(Mes)Si : (Mes=mesityl), which was found to be readily available on the thermolysis of the corresponding disilenes Tbt(Mes)Si=Si(Mes)Tbt, with several kinds of isocyanides bearing bulky aromatic substituents. The spectroscopic investigation on the resulting blue or greenish blue pastes revealed that the silylene adducts of isocyanides here obtianed were not the cumulative double-bond species but the novel silylene-isocyanide complexes. This is the first examples of isolated silyene-Lewis base complexes.3.The thermal reaction of an overcrowded silascylopropane derivative in the presence of elemental selenium resulted in the formation of silaneselone Tbt(Dip)Si=Se(Dip=2,6-diisopropyl-phenyl)stable in solution.As an extension of this research project, the double-bond species between germanium and heavier chalcogen atoms kinetically stablilized by taking advantage of the Tbt group, i.e.germanethiones, germaneselones, and germanetellones Tbt(R)Ge=X[X=S,Se, Te ; R=Tip or CH(SiMe_3)_2], were all synthesized and isolated as stable crystalline compounds. These results have been partially published as papers listed in the references. Less