Dehalogenating polycondensation

Figure 5.41 Polyquinoxaline syntheses by catalyzed dehalogenative polycondensation.

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 dehalogenating polycondensation of dihaloarenes to poly(arylene)s, involving reductive coupling with metals such as magnesium or zinc [scheme... 

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. 

An analogous synthetic approach that uses Ni(0)-catalyzed dehalogenative polycondensation. yielded, for example, yellow polymers 151 with = 8,000-13,600 and PDI = 1.3-2.1 by GPC (Equation (54)). " Comparison of the UV-VIS spectrum for the polymer with that for the model dimer was consistent with the presence of a... 

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]. 

Horhold and Rathe [248] reported that they have prepared poly(9-methylcarbazole-3,6-diyl-l,2dipenylvinylene). The polymer (M = 10,000) was formed by dehalogenating polycondensation of 3,6-bis(a,oc-dichlorobenzyl)-10,9-methylcarbazole with chromitm(II) acetate. This polymer was found to be also highly photoconductive. Its dark conductivity increases by doping it with arsenic pentafluoride [248]. 

Scheme 4.5 Ni-catalyzed dehalogenative polycondensation of p-dihalobenzene with Mg. Ni(II)Lm divalent Ni complexes such as NiCl2(bpy) (bpy = 2,2 -bipyridyl) and NiCl2(diphosphine). X = Br, Cl, etc.

Scheme 4.6 Ni-catalyzed dehalogenative polycondensation of p-dihalobenzene with Zn.

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. ... 

Both copolymers are thermally stable with initiation of thermal decomposition at about 250°C and residual weight of about 70% at 900° C as measured by TGA. The properties and structure of these copolymers as well as those of polyaromatics prepared by dehalogenation polycondensation are described in an adjacent paper [35]. 

One of the most useful methods of chemical synthesis is the Ni-catalyzed dehalogenation polycondensation of dihaloaromatic compounds [271] ... 

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],... 

Phenylic substituents at the vinylene positions — increasing both solubility of the polymer and stability of the double bond — can be achieved by reductive dehalogenation polycondensation of l,4-bis(phenyldichlormethyl)benzene derivatives with chromium(II)-acetate as reducing agent [44] (see Scheme 13). 

Curtis Method. McQain et al. [467] report that polymers are generated by FdQ2-catalyzed dehalogenation polycondensation of 2,5-bis(chloromercurio)-3-alkylthiophenes with Cu powder in pyridine (Fig. 15). Ester hmctional groups at the 3-position do not seem to be affected by the polymerization conditions. 

Thiophene-Pyridme. In an effort to combine the electron-donating properties of thiophene with the electron-accepting nature of j dine, Mitsuhara et al. [784] electropolymerized 2,5-, 2,6-, and 3,5-[di(2-thienyl)]pyridine derivatives. Others have carried out chemical polymerization of 2-(2-thienyl)pyridine and 2,5-di(2-pyridyl)thiophene by dehalogenative polycondensation of the corresponding dihaloaromatic compounds using a zero-valence nickel complex [785,786] (Fig. 49d). 

Yamamoto, T, K. Osakada, T. Wakabayashi, and A. Yamamoto Nickel and Palladium Catalyzed Dehalogenating Polycondensation of Dihaloaromatic Compounds with Zinc. A New Route to Poly(2,5-thienylene) and Poly(l,4-phenylene). Makromol. Chem., Rapid Commun. 6, 671 (1985). 

Yamamoto T, Osakada K, Wakabayashi T, Yamamoto A (1985) Nickel and palladium catalyzed dehalogenating polycondensation of dihaloanunatic compounds with zinc. A new route to poly(2,5-thienylene)s and poly(l,4-phenylene). Makromol Chem Rapid Commun 6 671-674... 

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