Polysilanes coupling reactions

Because the coupling reaction is usually carried out in excess sodium ([Na]o/[Si-Cl]o=1.2), degradation of the polymer is possible. We had prepared polysilanes and tested this possibility by their reaction with... 

Attempts have been made to prepare polysilanes containing the 8-dimethylaminonaphth-l-yl ligand.863 The coupling reaction of 8-dimethylaminonaphth-l-yl lithium with MeSiClj has given the dichlorosilane 909, whose mild reduction with Mg has surprisingly yielded the disilane 910 rather than the expected polysilane (Scheme 128). The formation of the disilane may be rationalized by the insertion of a transient silylene 904 into an Si-N bond of... 

Polysilanes with functionalities Z directly attached to the silicon main chain are generally more difficult to synthesize and less stable, due to the reactivity of both the Si-Z and Si-Si linkages. Such polymers are usually not accessible via the Wurtz-type coupling reaction, and alternative synthetic strategies (see Sections 3.11.4.1 and subsequent) or postpolymerization techniques have to be employed. 

Most polysilanes are synthesized by the Wurtz-type coupling reaction, which is non-stereospecific, and hence the configuration is usually undefined, although in a few cases, stereochemically defined polysilanes have been synthesized (ROP of all-anti l,2,3,4-tetramethyl-l,2,3,4-tetraphenylcyclotetrasilane99 101 and masked disilene polymerization).61... 

The main method used to synthesise polysilanes 10.7 involves the thermally induced Wurtz coupling reaction of organodichlorosilanes with alkali metals [eqn (10.7)]. Although improvements in this process have been reported e.g. by the use of ultrasound), the harsh conditions for this reaction tend to limit the side groups that can be successfully introduced to non-functionalised alkyl and aryl units and makes scale-up unattractive. 

Because of these limitations, considerable effort has been focused on the development of new synthetic routes to polysilanes. The early transition metal-catalysed dehydrocoupling process discovered in 1985 [eqn (10.8)] is potentially very attractive however, the molecular weights of the polysilanes formed to date are generally fairly low (Mn<8000)." The catalysts used for these coupling reactions are usually titanocene or zirconocene derivatives." " " ... 

Metalated halosilanes were postulated as intermediates in the reductive coupling reactions of dihalosilanes 39 to yield linear and cyclic oligo- and polysilanes (Scheme 12). 

Piezochromism, polysilanes, 3, 609 PIMS, see Photoionization mass spectrometry Pinacolboranes, cross-coupling reactions, 9, 170 Pinacolboronates, synthesis, 9, 167 Pinacol coupling... 

It should be noted that functionalised diacetylene monomers have also been used for coupling reactions with haloarenes. By reacting diacetylene-substituted p-aminoanilines [135] and diethynyl(methyl)( -octyl)silane [136] with diiodoarenes, polyamides and polysilanes have been prepared, respectively. 

R. G. Jones and S. Holder, Synthesis of polysilanes by the Wurtz reductive coupling reaction , in Reference 4, pp. 353-374. 

Fig. 2 Typical synthesis of a polystyrene-Z /6>ck-polysilane-Z7/6>c -polystyrene by a polymer coupling reaction...

SiH-functional poly(silylated) aromatic hydrocarbons are important starting materials for the preparation of arene-bridged polysilanes through thermal or catalytic dehydrogenative coupling reactions. 

The synthesis of polysilanes by the Wurtz-type reductive-coupling reaction is shown in Scheme 11.6. It is applicable to the synthesis of any polysilane, the substituents of which can withstand the harsh reaction conditions. This limits the systems to ones with aUcyl, aryl, silyl, fluoroalkyl, and ferrocenyl substituents but other structures are accessible through post-polymerization chemistry. ... 

Scheme 11.6. Synthesis of polysilanes by the Wurtz-type reductive-coupling reaction.

The Wurtz-coupling reaction of diorganodichlorosilanes is still the method applied most to synthesize non-branched polysilanes [30]. 

Besides the Wurtz-coupling reaction, other synthetic routes towards non-branched polysilanes have been reported, which overcome the drawbacks of polymodal molar weight distribution and low yield of the high molar mass fraction. However, so far the application of these routes has been very limited. The anionic ring opening polymerization of the strained 1,2,3,4-tetramethyl-1,2,3,4-tetraphenylcyclotetrasilane leads to poly(methylphenylsilane) in high yield but the starting cyclotetrasilane has to be prepared in three steps from diphenyldichlorosilane via octaphenylcyclotetrasilane [84] ... 

Synthesis of Polysilanes by Wurtz-type Coupling Reactions... 

In spite of its many drawbacks (as will be evident during the course of this discussion), the alkali metal-assisted Wurtz-type coupling reaction remains by far the most widely used procedure for the preparation of polysilanes... 

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