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