Dichlorosilanes coupling

WurtZ-Type Coupling of Dihalosilanes. Several approaches have been developed for the synthesis of polysdanes. However, the most commonly utilized method is based on the Wurtz-type alkah metal coupling of dichlorosilanes. Both homo- and copolymers can be prepared this way (eq. 10). 

Polymer Modification. The introduction of functional groups on polysdanes using the alkah metal coupling of dichlorosilanes is extremely difficult to achieve. Some polymers and copolymers with 2-(3-cyclohexenyl)ethyl substituents on siUcon have been made, and these undergo hydrogen hahde addition to the carbon—carbon double bond (94,98). 

The second approach to linear polysilanes is based on the modification of polysilanes prepared by the reductive coupling method. The severe conditions of this reaction allow only alkyl or aryl substituents at the silicon atom in the starting dichlorosilane. Therefore only alkyl or aryl substituted polysilanes are known. We have successfully prepared new polysilanes with pendant alkoxy and amino side groups. This approach allows fine tuning of the properties of... 

Jacobson-Stockmayer theory (L2.). Usually transfer and termination reactions in polymerization have energies of activation higher than propagation. Thus, we attempted coupling reactions at temperatures lower than usually applied. In order to assure the access of dichlorosilane to the surface of the sodium, the dispersion was continuously regenerated by ultrasonication. 

GPC traces of complete products of the reductive coupling of dichlorosHanes with Na In refluxing toluene. Hexylmethyl-dichlorosilane, phenylmethyldichlorosilane. 

GPC traces of products of the reductive coupling of hexylmethyl-dichlorosilane with Na in refluxing toluene. A, with rapid stirring B, with slow stirring. 

Matyjaszewski Krzysztof, Dorota Gresta, Hrkach Jeffrey S, Hwan Kyu Kim (1995) Sono-chemical synthesis of polysilylenes by reductive coupling of disubstituted dichlorosilanes with alkali metals. Macromolecules 28 59-72... 

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... 

Synthesis is typically by alkali metal-mediated coupling of dichlorosilanes or 1,2-dichlorodisilanes, although electrochemical coupling of chlorosilanes and dehydrocoupling of primary and secondary silanes also often lead to oligomeric (as opposed to high polymer) fractions. 

The most common route to polysilane-high polymers is by the Wurtz-type alkali metal-mediated polycondensation of dichlorosilanes. However, , u-dihalooligosi lanes can also be coupled in a similar manner. Wurtz-type polymerization of BrSiMe2SiR2SiMe2Br led to bimodal molecular weight distributions of alternating co-polymers of the type (SiMe2SiR2SiMe2) (R = hexyl or Bu),17 as in Equation (1). 

Synthesis of Polysilanes. The most commonly utilized method is based on the Wurt/ type alkali metal coupling or dichlorosilanes. Other synthesis methods include dehydrogenative coupling, ring-opening polymerization, polymerization of masked disilenes. electrochemical synthesis, and polymer modification. 

All of the polysilanes used in this study were prepared by the modified Wurtz-type coupling of substituted dichlorosilanes by sodium dispersion in an inert aromatic solvent as previously described (23.24). Poly(di-n-hexylgermane) was similarly prepared from di-n-hexyldichlorogcrmane (16). All of the polymer samples... 

A cyclic polydimethylsiloxane was also prepared by the end-to-end reaction, i.e., a,ft)-dianion-functionalized polymers, which are then cyclized simply by reaction with a difunctional electrophile to give a cyclic polymer. The cyclic polydimethylsiloxane was synthesized from a commercially available o. tw-dihydroxy-polydimethylsiloxane (M = 2.460 g/mol). The Unear precursor was deprotonated using sodium hydride in dilute THF (< 10 2 M) and then end-coupled using a dichlorosilane coupUng agent (Fig. 53). The uncy-clized anionic linear precursors are then removed by a macroporous anion exchange resin. The successful cyclization and purification is monitored by IR and 29Si NMR, GPC, and MALDI-TOF mass [176],... 

As shown in Scheme 3, the synthesis of a cyclo-l,3,5-trisila-2,4,6,7-tetrazane was accomplished by the coupling of a 1,3-dichlorosilane with a dilithium 1,2-hydrazine,63 64 whereas in the analogous reaction with pure hydrazine only the equivalent six-membered ring is obtained.64... 

The R1 values obtained for such phenylethynyl substituted siloxanes are higher then that reported for traditional aromatic-based systems [9] or the phenol modified ones (1.50-1.53) [10]. The synthesis of high refractive index (methyl)(diphenyle thenyl)-dichlorosilane via hydrosilylation was also described [1]. Such monomer was later hydrolyzed and condensed into silicone fluid. Similar process was also presented, applying silylative coupling process in the synthesis of an analogous (methyl)(phenylethenyl)diethoxysilane [11], so the two reactions shall be discussed in the following section. 

The sodium condensation reaction of a,co-bis(chlorosilyl)-substituted compounds and the coupling reaction of dilithio derivatives of compounds bearing 7t-electron systems with dichlorosilanes offer a convenient route to various silicon containing polymers. However, the polymers prepared by these methods always contain a small proportion of siloxy units in the polymer backbone, which would interrapt the electron delocalisation. Therefore, new synthetic routes to organosilicon polymers have been developed in which no alkali metal halide condensations are involved [6, 7]. We report syntheses of organosilicon... 

The coupling of dichlorosilanes (30 mmol) with excess of Me3SiCl (10 mol. eq.) led, after the passage of 4.2 F moP, to the respective trisilanes (Eq. 9) in isolated yields much higher than those obtained from chemical routes (Table 3). Both, A1 and Mg anodes gave similar results. 

Several studies of the mechanism of the sodium coupling reaction have been carried out, and a mechanistic model has emerged which accounts for most of the experimental observations. The reaction chain appears to be anionic in nature. The first step is believed to be the slow reaction of the dichlorosilane with sodium to give an anion (equation 34). The chain-extending process is the reaction of polymer silyl anions with dichlorosilane molecules (equation 35), followed by rapid reduction of the chlorine-terminated polymer to the anion (equation 36). Reduction must take place at the surface of a sodium particle. As polymerization occurs, some molecules may break free from the sodium surface once in solution away from the metal, chain extension would cease. This portion may give rise to the low-molecular weight polymer. Other molecules probably become entangled at the sodium surface and so cannot break free. They therefore continue to react with fresh dichlorosilane, and eventually... 

Polysilylenes are usually prepared by the Wurtz-type reductive coupling of dichlorosilanes with alkali metals. 

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