Polycondensation dehalogenation reactions

Such polycondensation dehalogenation reactions remain a commonly employed route to poly thiophene, and a range of solvents, halogenothiophene substrates, and other metal-based catalysts have been examined, as recently reviewed.29 For example, the reaction of 2,5-dibromothiophene with Ni(cyclooctadiene)2 and triphenylphosphine in DMF leads to an almost quantitative yield of polythiophene.30 Solid-state 13C NMR studies confirm exclusive 2,5-coupling of the thiophene repeat units in the polymeric product. The 2,5-dichlorothiophene monomer is less active as a substrate in such reactions however, the corresponding 2,5-diiodothiophene is reported to be a good substrate.31... 

Colon Method. 2,5-Dihalothiophenes were polymerized by a polycondensation dehalogenation reaction where Ni(0) was generated in situ by the reduction of NiG2 wifb Zn powder in the presence of triphenylphosphine in dimethylformamide (DMF), also known as the Colon method [428, 436] (Fig. 15). PoIy(3-alkythiophene)s were synthesized according to this method. Di-iodothiophenes were found to be more reactive than dibromoth-iophenes [273]. 

Such polycondensation dehalogenation reactions remain a commonly employed route to polythiophene and a range of solvents, halogenothiophene substrates, and other metal-based catalysts have been examined, as recently reviewed. For example, the reaction of 2,5-dibromothiophene with Ni(cyclo-... 

Another group of reactions can be classified as intermolecular dehalogenations or dehydrohalogenations, based on Wurtz-, Fittig-, Ullmann-, Grignard-, or Friedel-Crafts reactions. Thus, polyphenylenes may be obtained by polycondensations of p-dichlorobenzene in the presence of Na/K alloy83-85. ... 

The C-C coupling reaction between RMgX and R X is considered to proceed though an Ni(R)(R )Lm intermediate, and acceleration of the reductive elimination of R-R by coordination with olefinic or aromatic R X to Ni(R)(R )Lm is necessitated for a smooth catalytic reaction [15,16]. On these bases Ni-pro-moted dehalogenative polycondensation of dihalo organic compounds is suited to the preparation of 7i-conjugated aromatic and olefinic polymers. 

The reaction of Grignard reagents with 1,2-diisocyanobenzenes results in formation of quinox-aline oligomers up to the hexaoligomer. Reactions of 5,8-dibromo-2,3-diphenylquinoxaline with a zero-valent nickel complex afford poly(2,3-diphenylquinoxaline-5,8-diyl). Chemical and electrochemical dehalogenation polycondensations of 2,6-dibromoquinoxaline using nickel complexes afford poly(quinoxaline-2,6-diyl). ... 

Optically active l,l -binaphthols are among the most important chiral ligands of a variety of metal species. Binaphthol-aluminum complexes have been used as chiral Lewis acid catalysts. The l,T-binaphthyl-based chiral ligands owe their success in a variety of asymmetric reactions to the chiral cavity they create around the metal center [107,108]. In contrast with the wide use of these binaphthyls, the polymer-supported variety has been less popular. The optically active and sterically regular poly(l,l -bi-naphthyls) 96 have been prepared by nickel-catalyzed dehalogenating polycondensation of dibromide monomer 95 (Sch. 7) [109] and used to prepare the polybinaphthyl aluminum(III) catalyst 97 this had much greater catalytic activity than the corresponding monomeric catalyst when used in the Mukaiyama aldol reaction (Eq. 29). Unfortunately no enantioselectivity was observed in the aldol reaction. 

Poly(pyrazine-2,5-diyl) has been prepared by Yamamoto et al. [74] by organome-tallic dehalogenative polycondensation of 2,5-dibromopyrazine (Scheme 14.37). The reaction was performed by irradiating a mixture of 2.62 mmol 2,5-dibromopyrazine, 5.23 mmol bis(l,5-cyclopentadiene)nickel(0), and 5.23 mmol 2,2 -bipyridyl in a single-mode microwave reactor for 10 min, either in toluene or DMF solution. Under microwave conditions, the polymer was afforded in 83-95%... 

Novel organometallic poly(arylene)s with 1,3-type (cyclobutadiene)cobalt moieties 27 in the main chain are prepared by Ni(0)-mediated dehalogenative polycondensation of monomers having (cyclobutadiene)cobalt moieties [51], The polymers with of 20 kDa exhibit thermotropic liquid crystallinity. The synthesis of a variety of homometallic and heterometallic oligomers and polymers such as 28 is possible via nucleophilic aromatic substitution reactions of dichlorophenylene-Fe Cp and dihydroxyphenylene-Ru Cp complexes in DMF in the presence of K2CO3 [52]. 

Organometallic C-C coupling reactions have been used for the preparation of PPP. For example, Ni-catalyzed dehalogenative polycondensation of p-dihalobenzene with Mg gives PPP as shown in Scheme 4.5. ... 

Zero-Valent Nickel Complexes. A new polycondensation reaction uses the zero-valent nickel complex itself as the dehalogenation reagent [271,570,571] ... 

For the preparation of PAT (n = 1,6, 8,12) and of poIy(3-cyanothiophene) with high yields, a zero-valent nickel complex is also used [266]. Hexyl substituted oligo(thiophene)s (number of thiophene rings 6,9,12,15) can be prepared by the Ni(0)-catalyzed coupling reaction of a 5,5"-dibromo-3,3"-dihexyl-2,2 5, 2"-terthiophene) [572, 573]. PT derivatives having alkyloxy substituents at 3 positions are synthesized by dehalogenation polycondensation of the corresponding 2,5-dibromothiophene derivatives with zero-valent nickel complexes [247],... 

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