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R. Fischer, J. Baumgartner, G. Kickelbick, K. Hassler, C. Marschner:
"Adamantanes, nortricyclenes, and dendrimers with extended silicon backbones";
Chemistry - A European Journal, 10 (2004), 1021 - 1030.

By reaction of the hexabromoheptasilane MeSi(SiMe₂SiMeBr₂)₃ (1a) with H₂O, H₂S, NH₃, and H₂NMe the heptasilaadamantanes MeSi(SiMe₂SiMeO)₃ (4), MeSi(SiMe₂SiMeS)₃ (5), MeSi(SiMe₂SiMeNH)₃ (6a), and MeSi(SiMe₂SiMeNMe)₃ (6b), resp., were prepd. in good to moderate yields. Mol. structures of 4, 5, 6a, and 6b were detd. by x-ray crystallog. The symmetry of the cages is approx. C3v, and the geometry around the N atoms is essentially planar. Ab initio SCF/HF calcns. with the 6-31G* basis set confirm these results. Redn. of MeSi(SiMe₂SitBuBr₂)₃ (1b) with Li naphthalenide afforded the heptasilanortricyclene MeSi(SiMe₂SitBu)₃ (7). The ²⁹Si NMR spectrum of 7 consists of three signals with chem. shifts that agree closely with values predicted by ab initio calcns. ²⁹Si INADEQUATE spectra also strongly support the nortricyclene structure. Ab initio SCF/HF calcns. were performed for the parent mol. Si₇H₁₀, and the ring strain of the cage was estd. as 168.8 kJ mol^-1 by using the homodesmic reaction Si₇H₁₀ + 3Si₂H₆ --> Si₁₃H₂₈. Compd. 1a also served as the starting material for the prepn. of first-generation dendrimer 2a by reaction with six equiv Ph₂MeSiLi. Subsequent protodearylation with HBr and reaction with (Me₂PhSi)₂SiMeK afforded second-generation dendrimer 3. All dendrimers were characterized by multinuclear NMR spectroscopy.

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