Wurtz-coupling reaction

In addition to sodium, other metals have found application for the Wurtz coupling reaction, e.g. zinc, iron, copper, lithium, magnesium. The use of ultrasound can have positive effect on reactivity as well as rate and yield of this two-phase reaction aryl halides can then even undergo an aryl-aryl coupling reaction to yield biaryls. ... 

The main method used to synthesise polysilanes 10.7 involves the thermally induced Wurtz coupling reaction of organodichlorosilanes with alkali metals [eqn (10.7)]. Although improvements in this process have been reported e.g. by the use of ultrasound), the harsh conditions for this reaction tend to limit the side groups that can be successfully introduced to non-functionalised alkyl and aryl units and makes scale-up unattractive. 

A Wurtz coupling reaction of 9,10-dichloro-9,10-dimethyl-9,10-disilaanthracene (200) with sodium in toluene affords a bridged dimer (202) in 7% yield. The X-ray structure is given in Figure 14a. The reaction of a cis/trans mixture of 9,10-dihydro-... 

The use of cesium compounds in C—C bond formation reactions has so far been limited to a few cases. Vogtle and KiUener [21] observed that the use of cesium metal in the Mtiller-Rdscheisen procedure [22] of the Wurtz coupling reaction of p-xylylene dibromide, intended to yield [2 ]paracyclophanes 1, leads to the [23]paracyclophane lb with the highest yield compared to other alkali metals. The yields of the other cyclic compounds Ic-e thereby are much lower compared to the application of sodium metal (Fig. 1) [23]. 

Wurtz coupling reactions of chlorosilanes are the main route to the silicon-silicon bonded compounds. For example, hexamethyldisilane can be prepared by refluxing trimethylchlorosilane with lithium sand in THF (97%). Lithium may be substituted by sodium by using a mixture of HMPA-THF as the solvent. Linear and branched oligosilanes can be prepared by the same method (equations 55-57). 

Polysilylene Synthesis. Polysilylenes are synthesized by the Wurtz coupling reaction of dichlorodialkyl- or dichloroarylalkylsilanes with molten sodium in an aromatic solvent according to the following reaction ... 

In the Wurtz coupling reaction of dichlorosilanes with sodium to poly silanes [Eq. (42)], polysilanyl anions are considered to be crucial reaction intermediates in the propagation step and in the cyclization via back-biting (Scheme 23) 88). 

A classical method using Na- or Li-liquid ammonia (Birch reduction conditions) is effective for reductive dehalogenations of aryl and vinylic halides, but it is not always successfully applied to alkyl halides, although cyclopropyl halides and bridgehead halogens are exceptions.Under such conditions, the reactions are often accompanied by side reactions, such as elimination, the Wurtz coupling reaction, cyclization and reduction of carbonyl compounds. An example, a synthesis of pentaprismane (1), is shown in Scheme 4. ... 

A third synthetic route that has been successfully exploited in the formation of five- and six-membered heterocycles has been studied in an attempted synthesis of a borirene derivative. Reaction of phenylboron dibromide with tolan gives a mixture of products resulting from both haloboration and phenylboration 109). A Wurtz coupling reaction of the former derivative could generate a borirene derivative... 

Silicon heterocycles with different ring sizes have been synthesized by variations of the organometallic Wurtz coupling reaction. The method requires synthesis of intermediate organosilicon derivatives that can involve several steps. 

The derivatives of structural type (VII) may also be prepared by organo-metallic Wurtz coupling reactions as was the case for smaller ring sizes. 

Further support for the proposed mechanism is provided by the results of experiments involving phenylbromide instead of ethylbromide (Jj6). The polarizable TT electrons of this aryl compound allow it to effectively compete with styrene for the sites on the lithium surface and thus the Wurtz coupling reaction becomes dominant. Similar results were obtained with ethyltosylate. Although the reaction of tosylate with living polystyrene is rapid and quantitative, yielding ethyl capped polymers, its reaction with the monomer and metallic lithium produces only 10% of the ethyl capped polymers, the remainder being evolved as butane. Again, the aromatic nature of tosylate allows it to compete with styrene for the lithium sites. 

Further support for the proposed mechanism is provided by the results of experiments involving phenylbromide instead of ethylbromide88. The polarizable re electrons of this aryl compound allow it to effectively compete with styrene for the sites on the lithium surface and thus the Wurtz coupling reaction becomes dominant. Similar results were... 

It was shown that alkyl bromides react without a catalyst with allylmagnesium bromide in THF. However, because allyl bromide reacts quantitatively with magnesium in THF to give 1,5-hexadiene by a Wurtz-coupling reaction, allylmagnesium bromide can be obtained in this solvent only by solvent exchange ... 

The Wurtz-coupling reaction of diorganodichlorosilanes is still the method applied most to synthesize non-branched polysilanes [30]. 

Besides the Wurtz-coupling reaction, other synthetic routes towards non-branched polysilanes have been reported, which overcome the drawbacks of polymodal molar weight distribution and low yield of the high molar mass fraction. However, so far the application of these routes has been very limited. The anionic ring opening polymerization of the strained 1,2,3,4-tetramethyl-1,2,3,4-tetraphenylcyclotetrasilane leads to poly(methylphenylsilane) in high yield but the starting cyclotetrasilane has to be prepared in three steps from diphenyldichlorosilane via octaphenylcyclotetrasilane [84] ... 

A large excess of magnesium turnings is necessary to prevent the formation of biallyl (1,5-hexadiene) by a Wurtz-coupling reaction. Small magnesium turnings (3-... 

Higher members like [23](l,4)cyclophane (34) are available in a modified Wurtz coupling reaction [38]. Cram [32] described the complexation of only one benzene ring of 34, while Elschenbroich [39] succeeded in the complexation of the second and third benzene ring by variation of stoichiometry and prolonged reaction time (Fig. 6b). 

The end-groups of a sample of poly(methylphenylsilane) (PMPS), obtained by the Wurtz coupling reaction of diorganodichlorosilane followed by fractionation with methanol, were characterized by comparing the MAFDI spectra obtained with and without the addition of a specific alkaline salt (FiCl, KCl, or Nal) to the solution containing the sample and matrix. ... 

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