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  • 1995-1999  (2)
  • 1999  (2)
  • Chemistry  (2)
  • Titanverbindungen
  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 21-26 
    ISSN: 1434-1948
    Keywords: Silicon ; Silanes, sterically congested ; Tris(trimethylsilyl)silanes ; (Chloromethylene)ammonium chlorides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tris(trimethylsilyl)silyllithium (1) reacts with dialkyl(chloromethylene)ammonium chlorides (molar ratio 2:1) to give the (dialkylamino)bis(hypersilyl)methanes [(Me3Si)3Si]2CHNR2 (5a-c; a: R = Me, b: R = Et, c: R2 = [CH2]5). Due to the extreme bulkiness of the hemispherical (Me3Si)3Si substituents, the structures of these geminal bis(hypersilyl) derivatives are characterized by tremendous distortions of their molecular skeletons. This was confirmed by X-ray structural analyses of 5a and 5c, which revealed considerable elongations of the central Si-C bonds (5a: 2.01 and 1.95 Å; 5c: 1.99 and 1.97 Å) and an extreme widening of the Si-C-Si angles at the central sp3-carbon atoms (5a: 132.6°; 5c: 128.7°). By concentrated sulfuric acid, 5a is converted to give, after hydrolysis, the silanol (Me3Si)2Si(OH)-CH2Si(SiMe3)3 (13). The formation of 13 is discussed as proceeding through the transient silene (Me3Si)2Si=CHSi(SiMe3)3 (11), generated by a formal (dimethylamino)trimethylsilane elimination from 5a according to an acid-induced sila Peterson mechanism.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-1948
    Keywords: N-ligands ; Yttrium ; Samarium ; Ring-opening polymerization ; Lactones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of one equivalent of dilithiated O(SiMe2-Ap-H)2 [Ap-H = -N(2-amino-4-methylpyridine)] (1), generated in situ, with LnCl3 (Ln = Y, Sm) in THF affords O(SiMe2-Ap)2YCl(THF)2 (2) or O(SiMe2-Ap)2SmCl(THF)3 (3). In contrast, the reaction of one or two equivalents of dilithiated 1, again generated in situ, with LaBr3 in THF affords O(SiMe2-Ap)2)2LaLi(THF)3 (4). An X-ray structural analysis of 2 and 3 reveal the O(SiMe2-Ap)2- ligand to bind in a planar tetradentate manner. Equivalent Sm-N distances in 3 indicate a delocalized binding mode. Compound 2 reacts with Bu4NBH4, NaBH4 or LiCH(SiMe3)2 to give the corresponding “ate” complexes O(SiMe2-Ap)2Y(BH4)Cl(THF) Bu4N (5), O(SiMe2-Ap)2Y(BH4)2Na(THF)2 (6) and O(SiMe2-Ap)2Y(CH(TMS)2)2Li(THF)3 (7), respectively. The steric demand of the O(SiMe2-Ap)2- ligand is not large enough to stabilize monoalkyl or monoborohydride complexes. Complex 4 has been used as an initiator for the ring-opening polymerization of ε-caprolactone or δ-valerolactone. In both cases an almost linear relation between the monomer-to-initiator ratio and the molecular weight of the obtained polyester is observed. By conducting the polymerization in neat ε-caprolactone at room temperature a solid polyester block is formed after 3 min (300000 g·mol-1, Mw/Mn 2.3).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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