Wurtz-type couplings

Homocoupling of alkyl halides in aqueous media can be mediated 

The reductive coupling of allyl halides to 1,5-hexadiene at glassy C electrodes was catalyzed by tris(2, 2 -bipyiidyl)cobalt(II) and tris(4,4 -dimethyl-2, 2 -bipyiidyl)cobalt(II) in aqueous solutions of 0.1 M sodium dodecylsulfate (SDS) or 0.1 M cetyltrimethylammonium bromide (CTAB). An organocobalt(I) intermediate was observed by its separate voltammetiic reduction peak in each system studied. This intermediate undergoes an internal redox reaction to form 1,5-hexadiene 

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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). 

In a related coupling reaction, the reaction of diethyl 2,7-nonadien-l,9-dioate and Mg/MeOH generated a five-membered ring via coupling of an intermediate radical.Treatment of conjugated ketones with Smij in HMPA gave the coupled diketone via Wurtz-type coupling. 

In the Grignard reaction, which is very important in the manufacture of a variety of fine chemicals, the continuous reactor for production of the reagent consists of a column of magnesium particles through which a solution of the organohalogen compound in an ether-class solvent is passed. The continuous mode of operation reduces side reactions, particularly Wurtz-type coupling, which make many reactions impractical. 

Wurtz-type couplings have also been observed upon sonication of lithium in the presence of both organic halides (yields 36-73%) (218) and chlorosilanes or chlorostannanes (yields 42-94%) [Eq. (42)] (219). 

Scheme 5 Formation of polyfl, 1 -silole), 8, by Li-mediated Wurtz-type coupling.

It is noted here that the related poly(l,l-silole)s, polysilanes, in which each CRLJ is a silole ring catenating through the silicon atom, have been prepared by Wurtz-type coupling of dichlorosilole monomer54,55 and are described above in the section on Wurtz-type coupling (Section 3.11.4.1.1). 

Polysilanes with functionalities Z directly attached to the silicon main chain are generally more difficult to synthesize and less stable, due to the reactivity of both the Si-Z and Si-Si linkages. Such polymers are usually not accessible via the Wurtz-type coupling reaction, and alternative synthetic strategies (see Sections 3.11.4.1 and subsequent) or postpolymerization techniques have to be employed. 

Silole incorporation was noted above in Section 3.11.4.1.l.(iii) where poly( 1,1 -silole)s synthesized by Tamao and co-workers via Wurtz-type coupling were described. The related silole-incorporated polysilanes bearing silole units on every fifth silicon in a regular sequence prepared by Sakurai and co-workers using anionic ROP were described in Section 3.11.4.1.4. 

Most polysilanes are synthesized by the Wurtz-type coupling reaction, which is non-stereospecific, and hence the configuration is usually undefined, although in a few cases, stereochemically defined polysilanes have been synthesized (ROP of all-anti l,2,3,4-tetramethyl-l,2,3,4-tetraphenylcyclotetrasilane99 101 and masked disilene polymerization).61... 

Structural effects on properties were also studied in detail by a group from Tohoku University, who prepared poly(methylphenylsilylene) (PMPS Mv = 3,120, Mw/Mn = 1.76) and poly(phenylsilyne) (131 poly(penfafluorophenylrilyne)(PPS) 4/w = 1,090, Mw/M = 1.30) by Wurtz-type coupling using sodium and 18-crown-6 in hot toluene and compared their optical and electrical properties.359,360... 

This Wurtz-type coupling affords a mixture of air stable crystallizable products with two, three, four, and five fused rings (140, 141 -a, 141-r, 142-a,a, 142-//,.s and 143 respectively substituents / -Pr), separable by recycling HPLC. 

The Wurtz-type coupling reactions, which were one of the original methods for the formation of Ge-Ge bonds, are still in use.337 Various other synthetic techniques have been developed and improved upon in recent years as well. 

THF at -78 °C.[55] The reaction excludes the effect of the Wurtz-type coupling reaction,... 

Narrowly distributed Pl-ft-PS-i-PI triblock copolymer chains with both of their ends capped with bromobutyl groups were prepared by sequential addition of living anionic polymerization and terminated by excess of 1,4-dibromobutane (PS block Mw = 3.5 x 103 g/mol PI blocks Mw = 3.1 x 103 g/mol Mw/Mn = 1.12 The degree of end-functionalization was 92% characterized by HNMR). Figure 6 shows the SEC profile of such prepared triblock copolymer chains. The small but a detectable amount ( 5%) of Pl-i-PS-i-PI dimers, PI-Z>-PS-Z>-PI-c-PI-Z>-PS-Z>-PI, is presumably formed via the Wurtz-type coupling reaction. 

Trimethylsilylcycloalkenes. Some years ago Russian chemists prepared 1-trimethylsilylcyclohexene by coupling l-chlorocyclohexene with chloroli imethyl-silane mediated by sodium. More recent work indicates that this Wurtz-type coupling is a general and useful reaction (equation I).2... 

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... 

Dihalocycloalkenes, Heck couplings, 11, 315 (Dihalomethyl)silanes, lithiated, 9, 323 Dihalo-palladium(II) systems, liquid crystals, 12, 244 Dihalo-platinum(II) systems, liquid crystals, 12, 244 Dihalosilanes, Wurtz-type coupling... 

Carboranylene-1, l, 2,2-tctraructhyl-1,2-digcrruacyclobutanc has been prepared using the Wurtz-type coupling reaction of >-bis(chlorodimethylgermyl)-carborane with sodium (Equation 21) <2002IC3084>. 

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