Dehalogenation polymerization

Synthesis oxidative electropolymerization of phenazine in acid media in the dark [624], (The photoreduction of phenazine produces 1-hydroxyphenazine, and then poly(l-hydroxyphenazine) is formed.) Dehalogenation polymerization of 2,7-di-bromophenazine [595],... 

Ong and co-workers reported an alternative synthesis of poly(3,6-dialkylthieno[3,2- ]thiophene-co-bithiophene) (Scheme 17.7) [50]. In this case, a symmetrical monomer was constructed from the Stille cross-coupling of 2,5-dibromo-3,6-dialkylthieno[3,2- ]thiophene with 2-tributylstannylthiophene followed by bromination in the free a-positions with iV-bromosuccinimide. Dehalogenative polymerization (often termed Yamamoto polymerization [86]) was performed by refluxing in toluene in the presence of excess bis(cyclooctadiene)nickel(0) and 2,2 -bipyridyl afforded the product in 92 % yield. The number-average molecular weight was 12400 gmoP with a polydispersity of 1.6. 

A similar dehalogenative polymerization using Cu is possible when dichloroanthraquinone with electron-accepting -NO2 substituents, and poly-(anthraquinone-l,5-diyl) with two -NO2 groups at the 4,8-positions is obtained (M = 8600, Mw/Mn=1.5 (by GPC eluent = DMF vi. PS standards). Example 14 is based on refs. 77-79. 

The synthesis of a polyfluorene with para-carborane in the backbone was reported (compound 63 in Figure 26.25). This polymer was found to be a blue Ught-anitting material. The monomer l,12-fcM(7-bromo-9,9-dihexyl-9H-fluoren-2-yl)-c/o50-l,12-dicarbadodecaborane was first synthesized and then polymerized via a Ni(0)-catalyzed dehalogenative polymerization. Shifts in UV absorption and fluorescence emission indicate some involvanent of the p-carborane clusters in extending the conjugation (Peterson et al., 2009). 

Yamamoto and coworkers reported the synthesis of polyferrocenylenes with conductivities ranging from 10 to 10 S/cm via dehalogenation polymerization of dihaloferrocenes with magnesimn as shown in Scheme 20. The conductivity of this crystalline polymer was higher than that of the amorphous polyferro-cenylene. 

Various 1,5-dibromoquinoxalines have been polymerized by organometallic dehalogenation (Fig. 5.41). The reaction takes place in DMF with (1,5-cyclooctadiene) Ni(0) in the presence of 2,2 -bipyridine at 60°C for 48 h.168169 Highly conjugated acenaphthene quinoxalines were prepared by this procedure and exhibit photoluminescence peaks at 400 and 514 nm.170... 

The synthetic route represents a classical ladder polymer synthesis a suitably substituted, open-chain precursor polymer is cyclized to a band structure in a polymer-analogous fashion. The first step here, formation of the polymeric, open-chain precursor structure, is AA-type coupling of a 2,5-dibromo-1,4-dibenzoyl-benzene derivative, by a Yamamoto-type aryl-aryl coupling. The reagent employed for dehalogenation, the nickel(0)/l,5-cyclooctadiene complex (Ni(COD)2), was used in stoichiometric amounts with co-reagents (2,2 -bipyridine and 1,5-cyclooctadiene), in dimethylacetamide or dimethylformamide as solvent. 

As a consequence of facile homolytic cleavages, sulfonyl halides (I > Br > Cl F unsuitable) are able to add to unsaturated C—C systems. To prevent (or reduce) competing polymerizations, the additions of sulfonyl chlorides have been recommended to be carried out in the presence of copper(I/II) salts (Asscher-Vofsi reaction ). Comprehensive surveys have been published on the resulting j8-halogeno sulfones (or their vinyloguous compounds) as well as on their dehalogenation products (vinyl sulfones, 1-sulfonyl-l, 3-dienes, etc.). Table 5 reviews a series of sulfonyl halide additions and facile hydrogen halide eliminations. 

Fluorinated unsaturated carboxylic acids and their functional derivatives are prospective monomers for polymerization reactions. Their preparation fully relies on dehalogenation procedures dechlorination, and debromo- and dechlorofluorination are mostly employed (see Table 10). Fluorinated unsaturated acid halides can be prepared by dehalogenations with zinc46-61 or copper121 in aprotic solvents. 

Compounds 4 and 6 react with a-oleftns and 1,3-dienes on addition of excess trimethylaluminum, and especially on addition of triethylalu-minum and water. Dehalogenation takes place, presumably with formation of aluminoxanes (129), to give very active halogen-free homogeneous catalysts for the polymerization of a-olefins, particularly ethylene (see Section VII). 

In the case of MePhSiCb, the Wurtz coupling dehalogenation produces three fractions, containing low-molecular weight cyclics, intermediate molecular weight cyclic oligomers, and high polymeric materials." ... 

Cyanoborohydride and its modified reagents have been used for reductive dehalogenations. Thus, the combination of sodium or tetrabutylammonium cyanoborohydride, sodium or potassium 9-cyano-9-hydro-9-borabicyclo[3.3.1]nonanate [9-BBNCN] (2) or polymeric cyanoborane (3) in HMPA furnishes an efficient and mild system for the reduction of alkyl halides. The reagents are selective in that other functional groups, including ester, carboxylic acid, amide, cyano, alkene, nitro, sulfone, ketone, aldehyde and epoxide, are essentially inert under the reduction conditions thus, the reduction procedure is attractive for synthetic schemes which demand minimum damage to sensitive portions of the molecule. 

Deuteration of arenes, 206 Deuterium, role in nmr, 243 Dextrorotatory, 70 Diastereomers, 69 conformational, 80 Diastereoselective reactions, 91 Diazine, 458, 460 Diazomethane, 67, 353 Diazonium ions, 409 Diazonium salts, 416 Dicarboxylic acids, 342 Diels-Alder reaction, 154 Dienes, polymerization, 153j summary of chemistry, 154 Dienophile, 154 Dihalides, dehalogenation, 91 Dimethyl sulfoxide (DMSO), 305 Dioxane, 285 Dioxin, 447... 

---