Carbosilanes

Abstract

Carbosilanes are compounds in which the elements carbon and silicon occupy alternate positions in the molecular framework. Formal replacement of every second carbon atom in the diamond lattice by a silicon atom gives silicon carbide, which exists, however, in several modifications characterized by different stacking orders. The S i c lattice is the basis of most carbosilanes."] These are divided on the basis of structural differences into carborundanes, silascaphanes, and molecules that no longer contain elements of the silicon carbide structure. In the carborundanes the Si-C six-membered rings are arranged in the chair form, in the silascaphanes in the boat form. The molecular framework of the third group is derived from barrelane and asterane. The reactivity of the carbosilanes is determined mainly by the substituents on the skeletal atoms. The presence of SiH or Si-halogen groups leads to a high reactivity, while derivatives with organic groups on the silicon atoms and CH, or C H groups in the skeleton are much less reactive. However, even such CH2 and C H groups permit certain characteristic reactions. Because of their structural features and the range of substituents that can be introduced, the carbosilanes are presently of considerable interest with respect to technological developments as precursors for ceramics. I 1 : 1.25 Scheme 6 .

Gallium and Indium Arsanido Metalates: Compounds Derived from the Zinc Blende and Wurtzite Structure

“…With an average value of 249 pm the In±Cl bond lengths are somewhat longer than typical terminal In±Cl bonds containing indium centers with CN (coordination number) four [28]. Asterane structures in inorganic chemistry are known by the work of Fritz et al [29]. The carbosilane [Cl 2 Si(CH) 2 (SiCl) 2 [20], while the basic structural motif of the adamantane-like dianion of 3´THF, [(GaCl 2 ) 6 (As t Bu) 4 ] 2± , is the zinc blende structure (Figure 3, Scheme 1).…”

“…1 Computer-generated plot of the dimeric unit [1] 2 (SHELXTL [45], ellipsoids at the 50% probability level, H atoms omitted for clarity). [29]. c) Basic skeleton in [RMER'] 6 [20, 30±32].…”

Silicon-Based Polymer-Derived Ceramics: Synthesis Properties and Applications-A Review

“…However, polycarbosilanes have also become a focus of research efforts in recent years that have little or nothing to do with the prospect of developing ceramic precursors. 120,[191][192][193][194] These efforts appear to be stimulated by a more general interest in polycarbosilanes as a novel class of polymers that have potential for use in a much wider range of applications, as well as from a more fundamental perspective. In particular, it appears that chemists have begun to look at carbosilane chemistry for answers to important fundamental questions regarding the structures and properties of compounds and polymers that contain both carbon and silicon in their backbone structures.…”

Linear and hyperbranched polycarbosilanes with Si-CH2-Si bridging groups: A synthetic platform for the construction of novel functional polymeric materials

“…; (2) high conversion yield (ceramic yield) to high-purity SiC; and (3) the availability of a convenient crosslinking or thermosetting mechanism so as to allow retention of shape after processing and during pyrolysis. Various polycarbosilanes and polysilanes have been investigated for this purpose [1][2][3][4][5][6][7][8] ; however, the Yajima polycarbosilane, nominally '[SiH(CH 3 )CH 2 ] n ', has generated particular interest, due in part to its application as a precursor in the production of the only commercial SiC fiber, Nicalon 2 . 1 In this latter case the polymer employed, which is derived from [Me 2 Si] n by thermal isomerization, has a relatively high ratio of C to Si (2:1) and a complex structure which appears to contain largely carbosilane linkages.…”

“…Most of the other polycarbosilanes and polysilanes that have been studied also contain excess carbon; either this must be be eliminated on pyrolysis, resulting in a lower ceramic yield, or (more usually) it ends up in the ceramic product as free carbon. [1][2][3][4][5][6][7][8] The one exception is polymethylsilane, [SiH(CH 3 )] n , which has been produced from the corresponding dichloromethylsilane by alkali-metal (Wurtz) coupling 4 or by dehydropolymerization of methylsilane with transition-metal complex catalysts. 5 In this case, there is typically some methane loss on pyrolysis, leading to silicon-rich SiC.…”