Synthesis, Structure, and Functions of Low-Valent Organosilicon, -germanium, and -tin Compounds

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Synthesis, isolation, structure, and reactions of low-valent organosilicon compounds such as silicenium Ions and silylenes, and related germanium and tin compounds were investigated In order to discover the unique functions of these species. Following remarkable results were obtained :(1)The first vinylsilylenes and trlalkylsilylsilylenes were Isolated from photolysis of the corresponding trisilanes In 3-MP and 2-MeTHF matrices at 77K. Contrary to the theoretical predictions, vinyl substitution caused a significant red shift of the n(Sl)-3p(SI)transition of dimethylsilylene. Silylsllylelnes showed the transition band maxima at unusually long wavelength, suggesting the small S-T splitting.(2)A dialkylstannylene, 2, 2, 5, 5-tetrakis(trimethylsilyl)stannacyclopentane-l, l-diyl(1)was synthesized and characterized with NMR, high resolution mass, and UV-VIS spectroscopy, and X-ray crystallography, as the first monomeric dialkylstannylene with the coordination number of two In the solid state … More as well as In solution, In contrast to the structurally similar bls[bis(trimethylsllyl)methyl]stannylene(2), which Is known to be monomeric in solution but dimeric In the solid state. The newly designed cyclic ligand In 1 sterically protects the divalent tln atom from dimerization more effectively than two bls(trimethylsllyl)methyl substituents In 2.(3)The first ether complexes of silicenium Ions were observed as long-Hved species at low temperatures by ^1H, ^<13>C, and ^<29>Si NMR during the reactions of silanes with trityl tetrakis[3, 5-bis(trifluoromethyl)phenyl]borate(TFPB)In dichloromethane-d_2 in the presence of excess ethers, while trivalent silicentum Ions were not produced In the absence of any bases. The use of TFPB as a non-nucleophilic counter anion was crucial for the successful observation of the complexes ; sllyl perchlorates formed under the similar conditlons did not show significant Interaction with ethers. Clear evidence for the Intramolecular complexation of silicenlum Ions with alkoxy oxygens was obtained by monitoring the reaction of(3-ethoxypropyl)dlmethylsilane with trityl TFPB by NYIR. Less