Polyphenylene synthesis

Figure 71 Radical cation stair step mechanism of polyphenylene synthesis. (From Refs. 307 and 311.)...

Scheme 30.8 Hyperbranched polyphenylene synthesis by the single-monomer polycondensation method.

Shi J, Jim CJW, Mahtab F, Liu J, Lam JWY, Sung HHY, Williams ID, Dong Y, Tang BZ (2010) Ferrocene-functionalized hyperbranched polyphenylenes synthesis, redox activity, light refraction, transition-metal complexation, and precursors to magnetic ceramics. Macromolecules 43 680-690... 

In the Heck reaction the educt participates in the oxidative addition. The reductive elimination occurs without the target molecule. In the Ni catalyzed polyphenylene synthesis the target molecule participates also in the reductive elimination and halogen is removed in another reaction step. Fundamentally different classes of products can be expected if oxidative addition and reductive elimination involves fragments of the product and no halogen participate in the reaction. This can be expected with ArH activated reactions. The regioselectivity of activation of... 

Of particular synthetic importance is the coupling of aryl- and hetarylboronic acids to aryl- and hetaryl halides (or triflates), allowing for a convenient synthesis of biphenyls, even sterically demanding derivatives such as 14, hetaryl phenyls and Zj/ -hetaryls. With appropriately disubstituted aromatic substrates, the Suzuki coupling reaction can be applied in the synthesis of polyphenylene materials. 

Wessjohann LA, Ruijter E (2005) Strategies for Total and Diversity-Oriented Synthesis of Natural Product(-Like) Macrocycles. 243 137-184 Wiesler U-M,Weil T, Mullen K (2001) Nanosized Polyphenylene Dendrimers.212 1-40 Williams P, see Chhabra SR (2005) 240 279-315... 

Watt and Drummond, were considered to be inert for C-C bond forming reactions. However, by the expedient of transmetallation to Cu, Ni, Zn, Li, and Al, methodologies for the stereoselective synthesis of olefins and dienes, as well as unusual heterocycles, aromatics and their ring-annulated products are now available which are beginning to make impact on material science, e. g. synthesis of pentacenes and polyphenylenes. Takahashi and Li provide evidence that, with further developments in transmetallation and handling the zirconacycles outside of the Schlenk tube techniques, synthetic utility will increase and new catalytic reactions will be developed. 

H. Saadeh, T. Goodson, III, and L. Yu, Synthesis of a polyphenylene-co-furan and polyphenylene-co-thiophene and comparison of their electroluminescent properties, Macromolecules, 30 4608 4612, 1997. 

Another approach to CPL is the synthesis of conjugated polymers with intrinsic chiro-optical properties. A variety of polymers with CPPL have been synthesized so far. Most of them are based upon well-known conjugated polymers such as poly(thiophene)s [4,111], polyphenylene vinylene)s [123], poly(thienylene vinylene)s [124], ladder polymers [125], PPPs [126], polyphenylene ethynylene)s, [127] and poly(fluorenes) [128]. All of them have been modified with chiral side-chains, which induce the chiro-optical properties. 

Rehmann [90] has employed ultrasound to improve the yield of polyphenylene, thought at one time to have a future as a conducting material. Using dibromobenzene and a nickel complex catalyst he investigated both bath and probe systems and found that sonication led to improved yield when compared to the conventional synthesis (i. e. reflux) and also had the advantage of allowing the use of a lower temperature (20 °C). 

Scheme 3. Divergent synthesis of the polyphenylene dendrimers based on the Diels-Alder cycloaddition... 

Scheme 6. Palladium catalyzed synthesis of polyphenylene dendrimers...

Kimura et al. also presented the synthesis and characterization of a second-generation ruthenium(II) bis(terphenyl)polyphenylene dendrimer 52, an attractive molecule with regard to its electrochemical and photochemical pro-... 

A wide range of other monomer units have been employed in the synthesis of hyperbranched macromolecules and the range of structures obtained is nearly as diverse as those for dendritic macromolecules. For example, hyperbranched polyphenylenes [93], polyesters [104, 107-109], polyethers [110-112], polyamides [113], polysilanes [114], polyetherketones [100], polycarbazoles [115], etc. [116-118] have been prepared. Interestingly, a number of groups have also used growth processes other than condensation chemistry to prepare hyper-... 

Polyphosphazenes and cyclophosphazenes are almost unique as carrier molecules for transition metals because of the wide range of binding sites that can be incorporated into the phosphazene structure. The substitutive mode of synthesis described earlier allows a structural diversity that is not found, for example, in polystyrene, polyphenylene oxide, or other organic carrier polymers. 

The convergent synthesis of a range of aryl ester dendrimers with peripheral tetrathiafulvalene units was also reported (Devonport et al. 1998). The dendrimers acquire some amount of the cation-radical tetrathiafulvalene tips on reacting with iodine in solutions. Another promising material is polyphenylene dendrimers functionalized with benzophenone units. On being transformed into the potassium ketyl derivatives, the dendrimers bring forth intermolecular biradicals. These technically attractive species contain four-membered cycles that coordinatively combine two potassium cations... 

Finally, just a few words dedicated to the synthesis of polyphenylenes, extremely important polymers, and in particular substituted polyphenylenes such as PPV, which exhibit superb thermal and chemical resihence, semiconduchng properties upon doping and applicahons such as OLEDs. Contrary to their linear acenes counterparts, long polyphenylenes can be obtained e.g., by Bergman s method consisting in the thermal cycloaromatization of enediynes (Lockhart et al, 1981). 

Hyperbranched polymers are formed by polymerization of AB,-monomers as first theoretically discussed by Flory. A wide variety of hyperbranched polymer structures such as aromatic polyethers and polyesters, aliphatic polyesters. polyphenylenes, and aromatic polyamides have been described in the literature. The structure of hyperbranched polymers allows some defects, i.e. the degree of branching (DB) is less than one. The synthesis of hyperbranched polymers can often be simplified compared to the one of dendrimers since it is not necessary to use protection/deprotection steps. The most common synthetic route follows a one-pot procedure " where AB,-monomers are condensated in the presence of a catalyst. Another method using a core molecule and an AB,-monomer has been described. ... 

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