Polysilane oligomers

Photochemical transformations of cyclic and short chain polysilane oligomers have been intensively investigated (39). Irradiation of these materials in the presence of trapping reagents, such as silanes or alcohols, has suggested that substituted silylenes and silyl radicals are primary reactive intermediates. The former have been... 

Research on polysilane oligomers and polymers has been the major driving force for the paradigm shift to a new model of rotational conformations.57 58 Until very recently, the structures of polysilanes were mainly described in terms of the older anti-gauche model. This is now known to be incorrect, and as a result nearly 20 years of research will probably need to be reinterpreted. 

Ground States and Ionization Energies of Polysilane Oligomers... 

Kunai A, Kawakami T, Toyoda E, Ishikawa M (1991) Electrochemistry of organosilicon compounds. 2. Synthesis of polysilane oligomers by a copper electrode system. Organometallics 10(6) 2001-2003... 

Electrochemical synthesis of tetra and pentasilanes. Larger polysilane oligomers could also be obtained using the aluminum sacrificial anode technique. Thus, the electrolysis of 1-chloro-l-phenyltetramethyldisilane, electrochemically prepared as described above, led to the corresponding tetrasilane in 85 % yield (Equation 14). 

Thus, the sacrificial anode method allows polysilane oligomers to be built up in a stepwise fashion. 

The sacrificial anode electrochemical synthesis under controlled current seems to be a simple alternative to the use of akali metals, especially for the synthesis of di-, tri-, polysilane oligomers and polymers in high current efficiency and yield. This method is easy and inexpensive the reaction only needs a bar of a common metal such as Al, Mg, Cu it runs at room temperature a stabilized regulated supply is convenient not only because the reaction can be stopped instantly, but because, when needed, the dependency of the selectivity upon the quantity of electricity and upon the nature of the electrodes makes the reaction easy to control. Moreover, extrapolation to an industrial scale can be anticipated. 

At present, the only synthetic method leading to high molecular weight polysilanes is based on the Wurtz condensation reaction between dichlorodisubstituted silanes and alkali metals (low molecular weight oligomers were also prepared by dehydrogenation of secondary... 

We have been recently studying new pathways leading to polysilanes with low polydispersity and controlled structures. Our research is focused on three areas. The first one is low temperature reductive coupling in the presence of ultrasound. This leads to monomodal polymers with molecular weights in the range from Mn=50,000 to Mn=300,000 and polydispersities as low as Mw/Mn=1.20 (in addition to usually formed cyclic oligomers). 

Oxidation state, nickel, 170, 198, 202 Oxidative addition, 11, 20, 21, 293 Oxidative cleavage, polysilane, 153-154 Oxidative coupling, 171-173, 179-182 in C12-oligomers, 173, 188, 207, 209-210 electronic and steric factors, 198, 200 modelling, 176... 

In summary, the production of substituted silylenes and silyl radicals upon exhaustive irradiation at 254 nm of polysilane high polymers suggested that the polymer photochemistry resembled that previously reported for short chain acyclic and cyclic oligomers (39). More recent experiments, however, have suggested that the photochemical mechanism for the degradation of the high polymers is more complex than first envisioned (vide infra) (48). 

In recent years, dehydrocoupling reactions catalysed by early transition metal complexes have become an increasingly important method for generating catenated species of the p-block elements. In addition to producing cyclic oligomers, this approach is used to prepare linear oligomers and polymers such as polysilanes and polystannanes of the type H(MR2) H (M = Si, Sn) (see Section 10.1.4). ... 

Interest in polysilanes was aroused in 1975, when Yajima found that the permethyl polymer (Me2Si) , or its cyclic oligomer (Me2Si)6, could be transformed into silicon... 

Figure 5.1 Number of papers published on polysilane polymers and oligomers per year, plotted against time, showing the dramatic growth in the literature since 1984.

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