Polysilane synthesis

Figure 8 Schematic diagram of experimental setup for photo-CVD polysilane synthesis.

Bis(guanidinato)bis(benzyl) complexes, with Zr(IV), 4, 776 Bis(heteroarene) vanadium complexes, preparation, 5, 48 Bis(heteroatom) polysilanes, synthesis, 3, 584 Bis(iV-heterocyclic carbene) ligands, in silver(I) complexes,... 

During the last years several synthetic pathways to various polysilane backbones have been extensively studied. One interesting polysilane synthesis has been developed based on the disproportionation of chloromethyldisilanes, which are byproducts of the industrial chloromethylsilane production (Miiller-Rochow Synthesis) [1]. 

In addition to these general synthetic procedures, other methods of polysilane synthesis include electrochemical reduction of diorganodichlorosilanes [22], condensation reactions between appropriate acyclic difimc-tional reagents such as Li(Ph2Si)5Li and Cl(Me2Si)5Cl [4]. These latter methods are not discussed here. 

A typical procedure of polysilane synthesis by this methodology is as follows ... 

Although several improvements have been effected in the basic Wurtz-type reaction it must be mentioned that there is still not a single universal synthetic protocol that allows a high yield, monomodal, high-molecular-weight polysilane synthesis. For every new system that needs investigation, the optimum reaction conditions have to be experimentally determined. 

Polysilane Synthesis. The synthesis of poly(phenylmethylsilane) was carried out by the Wurtz coupling of phenylmethylchchlorosilane assisted by ultrasonication (20). First, sonication at 40% amplitude for twenty minutes was used to disperse sodium metal in toluene. Then, the silane monomer was added to this dispersion over a thirty-minute period. The reaction continued with sonication at 20% amplitude for one hour. A 50/50 ethanol/water mixture was used to quench the reaction. 

ABSTRACT. Polysilanes, (-SiRR -)n, represent a class of inorganic polymers that have unusual chemical properties and a number of potential applications. Currently the most practical synthesis is the Wurtz-type coupling of a dihalosilane with an alkali metal, which suffers from a number of limitations that discourage commercial development. A coordination polymerization route to polysilanes based on a transition metal catalyst offers a number of potential advantages. Both late and early metal dehydrogenative coupling catalysts have been reported, but the best to date appear to be based on titanocene and zirconocene derivatives. Our studies with transition metal silicon complexes have uncovered a number of observations that are relevant to this reaction chemistry, and hopefully important with respect to development of better catalysts. We have determined that many early transition metal silyl complexes are active catalysts for polysilane synthesis from monosilanes. A number of structure-reactivity correlations have been established, and reactivity studies have implicated a new metal-mediated polymerization mechanism. This mechanism, based on step growth of the polymer, has been tested in a number of ways. All proposed intermediates have now been observed in model reactions. 

As the low temperature synthesis yields a more homogenous polymer with respect to polydispersity and molecular weight, toluene can be exchanged by lower boiling solvents such as, e.g. THE Solvent effects, due to polarity and stabilization of the active species in the polymerization, are marginal compared to the temperature effect. The results of a Wurtz-type polysilane synthesis conducted at ambient temperature are given in Table 1, illustrating the low yields and PDI [19]. 

The lack of sufficient control of molecular weight distributions, molecular weight and polymer structure of polysilanes via a Wurtz-type coupling reaction led Sakurai and co-workers to develop an alternative method for polysilane synthesis in 1989 [31],... 

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