Silanes Carbosilanes

The interaction of polysilanes with X-ray photoelectrons (XPS) has been used for theoretical studies" and for analytical purposes.19 Seven polymers with silane, carbosilane, and siloxane fragments—(-Si(CH3)2-)n (PDMS),... 

The disadvantages of the synthesis routes 1-4 are the application of highly reactive and expensive metals (Li, Na, K, Mg) and the enormous quantity of solvents. Particularly, as result of the dehalocoupling reactions, the polymers are unreactive at room temperature. To overcome these problems we synthesized spinnable reactive poly(silanes/-carbosilanes) via heterogeneous catalytic disproportionation of methylchlorodisilanes which have been wasted as a byproduct of the "Direct synthesis" of methylchlorosilanes so far. 

Poly(silanes/-carbosilanes) and Their Conversion into SiC Fibers 721... 

The first type of polycarbosilane synthesized by using ADMET methodology was a poly[carbo(dimethyl)silane].14c Linear poly(carbosilanes) are an important class of silicon-containing polymers due to their thermal, electronic, and optical properties.41 They are also ceramic precursors to silicon carbide after pyrolysis. ADMET opens up a new route to synthesize poly(carbosilanes), one that avoids many of the limitations found in earlier synthetic methods.41... 

For carbosilane dendimers using an iterative alkenylation/hydrosilation sequence, see (a) Silane Dendrimers, A.W. van der Made, P.W.N.M. van Leeuwen,/. 

Phenolic substrates are not readily reduced to benzene derivatives, and this fact can be used to effect the transformation of methyl or benzyl ethers of phenols to their silyl ethers with elimination of CH4 or toluene as the only by-products. These studies include detailed mechanistic studies that support and corroborate our experiments and support the silane activation mechanism. The reaction is clean and high yielding enough to be applied towards the functionalization of the periphery of carbosilane dendrimers with perfluoroaryl borane moieties (Scheme 25).196... 

The carbosilane monomer, H2MeSiCH2CH2SiH3, contains both a secondary and a primary silicon center. After about 48 h with Cp2TiMe2 or Cp2TiCl2/ BuLi at r.t. the dehydrocoupling reaction occurred at the primary silane center to give a polysilane with a substituent at each silicon center that contained a tether to the secondary silane center. The initial polymer had a Mw of approximately 1000. After another 72 h at r.t., the... 

Recent studies on the direct reaction of elemental silicon with alkyl chlorides such as methyl chloride, activated alkyl chlorides, polychloro-methanes, (chloromethyl)silanes, (dichloromethyl)silanes, etc. are summarized in this review. In the direct reaction of elemental silicon with activated alkyl chlorides and polychloromethanes, the decomposition of the reactants can be suppressed and the production of polymeric carbosilanes reduced by adding hydrogen chloride to the reactants. These reactions provide a variety of new organosilicon compounds containing Si-H and Si- Cl functionalities, which should find considerable application in the silicone industry. 

SCHEME 18.10 Formation of polycarbosilanes by Pt-catalyzed hydrosilylation of vinyl-silanes. The catalyticaUy active species is [PtCb] which is in situ generated by reduction of HjPtClj with PrOH. Characteristic reaction steps are A Ugand substitution, B oxidative addition of Si-H, C H-migration, and D reductive eUmination of the carbosilane. ... 

A first approach to obtain silicon-containing surfactants without Si-0 bonds was made by Dow Corning [4, 5]. They reacted carbosilanes with several a-olefins containing reactive (e g., epoxy-fiinctional) moieties, catalyzed by platinum complexes. The surfactant properties and high stabilities of these compounds indicated a promising solution. However, the corresponding carbosilanes as precursors were synthesized via a Grignard reaction, so these silane surfactants were difficult and costly to produce. 

Hydrosilylation of unsaturated organosilicon compounds has also found several applications in molecular and polymer organosilicon chemistry. In particular, the addition of polyfunctional silicon hydrides to poly(vinyl)organosiloxane, catalyzed exclusively by Pt compounds and providing an activated cure for silicon rubber [10], has been of great practical importance. Hydrosilylation of the vinyl group at silicon seems to be effective synthetic method for preparation of oligomers and polymers with a linear or cyclolinear stmcture (polyhydrosilylation), and can occur either via the addition of dihydro-carbosilanes and -siloxanes to divinyl-silanes and -siloxanes [25, 26] or by intermolecular hydrosilylation [4] (eq. (1)). 

By carbosilanes we mean compounds with alternate carbon and silicon atoms in the molecule these may be linear (e.g., Cl3SbCH2-SiCl2-CH2-SiCl3) or cyclic [e.g., (SiCh-CfB ], the latter being termed cyclocarbo-silanes (23). Compounds which consist mainly of carbon atoms, between which a silicon atom is inserted as a hetero-atom, are thus excluded from consideration here. So, too, are polymeric carbosilanes, which have recently been reviewed elsewhere (59a). 

The decomposition chemistry of most polysilanes above 300 °C is quite complex and involves restructuring of the polymer backbone as well as substantial cleavage of the side groups. Generdly a poly(alkyl)silane must go through a carbosilane intermediate prior to formation of the SiC network (Kumada rearrangement) [125] ... 

Results of these investigations allowed one to propose two different mechanisms for the generation of carbosilane units in poly(chloromethyl) silanes. 

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