Poly dehydrogenative coupling

In the course of studying the reactions of Si-H compounds with dialkyltitanocenes, with a view to the synthesis of new hydridosilyltitanocene complexes, we adventitiously discovered that phenylsilane undergoes facile, quantitative dehydrogenative coupling to a linear poly(phenylsilylene) under the catalytic influence of dimethyltitanocene. The ease with which this reaction proceeds initially induced us to underestimate the significance of the observation. 

Among the various synthetic procedures for polysilanes is the Harrod-type dehydrogenative coupling of RSiH3 in the presence of Group 4 metallocenes (Reaction 8.1) [5,6]. One of the characteristics of the product obtained by this procedure is the presence of Si—H moieties, hence the name poly(hydrosilane)s. Since the bond dissociation enthalpy of Si—H is relatively weak when silyl groups are attached at the silicon atom (see Chapter 2), poly(hydrosilane)s are expected to exhibit rich radical-based chemistry. In the following sections, we have collected and discussed the available data in this area. 

TABLE 5. Representative examples for the preparation of poly(dialkyl)stannanes by Wurtz-type coupling A, Sml2-induced reduction B, electrochemical reduction C and dehydrogenative coupling D... 

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

Scheme 3. Synthesis of boron-modified poly(silylcarbodiiniides) by a dehydrogenative coupling of B(C2H4SiH3)3 with cyanamide, H2N-CN. Molar ratios of I 0.5 to 1 3 were chosen. The indexes N1 - N6 give the numbers of nitrogen atoms per boron atom. Chemical compositions range from (C6.5H2oNSi3B) (H-Nl) to (CgHisNjSisB) (H-N6). Likewise, boron-modified poly(silylcarfoodiimides) were obtained from B(C2H4Si(CH3)H2>3 [10],...

Stiubianu, G. Racles, C. Cazacu, M. Simionescu, B. C., Silicone-Modified Cellulose. Crosslinking of Cellulose Acetate with Poly[dimethyl(methyl-H)siloxane] by Pt-Catalyzed Dehydrogenative Coupling. J. Mater. Sci. 2010,45,... 

This poljunerization can be applied to a wide range of condensations between diethynyldiphenylsilane and aromatic halides including p3rridine and thiophene derivatives (13) (84). It was reported that dehydrogenative coupling of phenylsi-lane with m-diethynylbenzene in the presence of MgO to provide poly(silylene-m-diethynylenephenylene) (14) (eq. 14) (85,86). 

These polymers do not contain a functional group within the polymer chain but are classified as condensation polymers, since water is split out during the polymerization process. Another example is poly(p-xylene). which is produced by the oxidative coupling (dehydrogenation) of p-xylene ... 

Organic compounds having labile hydrogen atoms, such as phenols, anilines, and acetylenes, are also oxidatively polymerized by metal-complex catalysts (Eqs. 1-3). The oxidative coupling is a dehydrogenation reaction the polymer chain produced contains the dehydrogenated monomer structure as a repeating unit. As a remarkable example, poly(phenylene ether), one of the... 

Beller and coworkers recently reported a new strategy for the synthesis of poly-substituted anilines based on a three-component-coupling reaction and a domino deprotec-tion/aromatization reaction (equation l)44. A mixture of O-benzyl carbamate, p-toluene-sulfonic acid, aldehyde, AC2O and dienophile in /V-rnclhy I pyrrol idone was allowed to react for 24 h at 120 °C, followed by Pd/C catalyzed dehydrogenation in triglyme at 140 °C. A variety of tri-, tetra- and penta-substituted anilines were efficiently created by this domino process. 

The PPEs [14, 35, 36], which are dehydrogenated analogs of the poly(p-phenylene vinylene) s, display desirable optoelectronic properties that have found extensive use as emissive materials [37, 38]. PPE preparation is dominated by the Sonogashira Pd/Cu-catalyzed cross-coupling of aryl haUdes and terminal alkynes [39]. However, polymerizations under these conditions rarely achieve a high molecular weight, and defects such as diyne formation and alkyne crosshnking in the polymer backbone are endemic [14, 40]. Alkyne metathesis was envisioned as a complementary method to PPE synthesis, with much success. 

---