Polysilanes characterized

Silenes derived from aromatic di- or polysilanes have been characterized in particular by the ene-type reactions they undergo when treated with isobutene or acetone. Recently, Leigh80 observed the first reported case of one of these silenes undergoing [2+2] cycloaddition (21% yield) with acetone. The ene product, the only product previously detected from the reaction of such silenes, was formed in 41% yield, as shown in Eq. (33). 

If the alkyl substituent in a dialkyl substituted polysilane is either too short or is branched, it cannot pack properly to allow side chain crystallization, and hence, one would expect very different, properties from PDHS and its higher homologs. In order to study this possibility, we synthesized and characterized the di-n-butyl (PDBS), di-n-pentyl (PDPS) and di-5-methylhexyl polymers (PDMHS). 

Although considerable interest exists in the polysilanes the number of systems that have been investigated is limited. Thus, a need to prepare and characterize additional polysilane copolymers is readily apparent. It is expected that systematic investigations, as presented in this report, will yield additional and valuable insight into the unique behavior of this class of polymers. 

Polysilanes, whose heavier analogues have not yet been structurally characterized, include ... 

This knowledge and understanding may be helpful to characterize local conformations of other optically active polysilanes in solution. For example, poly(methyl-(-)-(3-pinanylsilane) [(+)-7 Mw = 10,200] prepared by Shinohara and co-workers.281 showed a bisignate CD band at 280 and 303 nm, associated with a broad UV absorption at 300 nm in chloroform at 15°C. Since the spectroscopic features are quite similar to those of i,28d-28e it is possible that the main chain in 7 may contain diastereomeric helical motifs with opposite screw senses and different screw pitches. 

There have been very few reports of polysilanes containing a carbon functional group such as unsaturated groups directly attached to the silicon main chain. This appears to be due to the difficulties in synthesis and characterization due to instability of these compounds. These polymers are expected to show significant differences to conventional polysilanes in their properties due to the interaction of main-chain cr-electron and side-chain 7r-electron systems. 

When COMC II (1995) was published, two general types of thermochromism (reversible) had been recognized for polysilanes on lowering the temperature a gradual bathochromic transition, and an abrupt transition to longer wavelength absorption. From the vast amount of experimental data now accumulated, five different types of thermochromic behavior on cooling can be characterized ... 

Demoustier-Champagne, S. Devaux, J. Polysilanes and copolymers synthesis and characterization. In Recent Research Developments in Polymer Science-, Pandalai, S. G., Ed. Transworld Research Network Trivandrum, 1998 Vol. 2, pp 1—27. 

We have recently synthesized and characterized a variety of soluble, substituted polysilane homopolymers by the condensation of appropriately substituted methylsilyl dichlorides with sodium dispersion as shown below and in Table I... 

Soluble and well-characterized polygermane homopolymers. (R Ciel,. and their copolymers with polysilanes have been prepared by the alkali metal coupling of diorgano-stbstiluled dihalogermancs, via clectrochemicul methods, and by tnmsition-metal catalyzed routes, as with the synthesis of polysilanes. 

The polysilanes are characterized by strong two-photon absorptions which lead to the production of a strong induced birefringence (An — 0.03 632.8 nm) caused by anisotropic photodestruction. The spectral response of the two-photon induced birefringence identical to that determined by two-photon fluorescence excitation. In each case a strong resonance occurs around 570 nm ( 4.28 eV... 

The calculations also predict that polysilane should have a higher equilibrium flexibility than polyethylene,178 and solution characterization techniques could be used to test this expectation. Dynamic flexibility can also be estimated from such energy maps, by determining the barriers between energy minima. Relevant experimental results could be obtained by a variety of dynamic techniques.179... 

Various methods may be used to examine configurations of polysilanes, but 29Si NMR spectroscopy has been the most useful. Silicon-29, like carbon-13, has spin 1/2 and a relatively low abundance, 4.7%. Nuclear magnetic resonance (NMR) spectroscopy using 29Si has been important for the characterization of siloxane polymers, and is proving to be equally useful for polysilanes. 

Platinum complexes, 39-43 Pnicogen atoms coordinated to E-E bonds, homoleptic dielement compounds with, 61-65 Polysilanes, 1-52 characterization, 34-37 mechanistic proposals, 13-18 Primary alkylsilanes, condensation, 23 Primary arylsilanes, 18-22 Primary silanes, 18, 22-24 condensation by metallocene catalysts, 19 Protic reagents, 170 2-Pyridylboronic esters, 223... 

The synthesis and characterization of polyacetylene (PA) provided new incentive for understanding 7r-electronic spectra, electron-phonon interactions and electronic correlations[l, 2, 14]. The electrical conductivity of chemically doped PA rivals that of metals. Families in Fig. 2 such as polydiacetylenes (PDAs), poly thiophenes (PTs), cr-conjugated polysilane (PSs) and polyparaphenylene vinylene (PPVs), among... 

But till now only methods involving an in situ formation of deprotonated 1 have been described. In this paper we present a procedure leading to pure, isolated 1-hydroxyalkyl-polysilanes 1. In presence of base fliey are easily converted into transient silenes, which were characterized by various dimerization and addition reactions. The availability of isolated 1 in the synthesis of silenes according to the Peterson concept offers the possibility of a free choice of the solvent and the base used to initiate the silanolate elimination. With respect to the significance of the reaction medium for the silene generation and its subsequent reactions, this is of particular importance. 

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