Phenylenes attempted syntheses

Marvel et al. 2471 attempted synthesis of poly(p-phenylene) from poly(l,3-cyclo-hexadiene), produced by Ziegler initiation ... 

Another carbonyl group derivative which forms an imidazole ring with a diamine is 5,iS-dimethyl-Af-tosyliminodithiocarbonimidate (76.10), which is useful in the synthesis of 8-aminopurines. In an attempt to prepare a l,S-benzo-diazepine, the chloroaldehyde (76.11) was stirred or warmed with o-phenylene-diamine but the main product was the benzimidazole. 

Poly(p-phenylene vinylene) (PPV) is a conjugated polymer, which becomes conductive by the addition of electron donors or acceptors [114, 115], Several methods have been reported for the synthesis of PPV [3, 4, 6], Direct chemical polymerization, which was used in the first attempt of synthesizing PPV, gave a product in the form of an insoluble powder that limited the use of the polymer in many applications [116], The most popular method for the preparation of PPV is base-induced polymerization of sul-fonium salt monomer in aqueous solution [114-118], In this method, PPV films are obtained from the precursor polymer after thermal elimination of the sulfonium groups. PPV has also been prepared electrochemically by reducing p-xylene-bis-(triphenylphosphonium). Two approaches are generally used for the synthesis of PPVs the Wessling... 

The preparation of poly(2,5 dimethoxy phenylene vinylene)(DM-PPV) utilized the xanthate precursor route. Many similarities exist between the PPV xanthate thermal elimination and this PPV derivative. Previous studies had attempted to synthesis DM-PPV using the SPR method. The SPR resulted in gel formation during dialysis so that film casting was not possible. The XPR was successful in preparing precursor films that can be thermally converted to DM-PPV. The derivatives of PPV are useful to prepare a polymer with a shift in the absorbance and photoluminescence maximum. DM-PPV exhibits an 100 nm red shift as compared with PPV synthesized via the XPR. 

Attempts to synthesize aromatic polysulfides by electrophilic substitution methods have failed to produce linear high molecular weight polymers. During the past three decades a systematic approach has been taken for the synthesis of aromatic polysulfides. The nucleophilic reaction of sodium sulfide with p-dichlorobenzene to give poly(phenylene sulfide) has been a successful process. The polymer produced by this method is abbreviated as PPS and has been commercialized by Philips Chemical Company under the trade name Ryton (reaction 24)... 

A mixed cyclothiophene including phenylene units was synthesized by Tobe et al. [423], Macrocycle 4.55 (Chart 1.56) was made, which includes four alternating 2,5-thienylene and 1,3-phenylene units and is similar in shape to cyclo [8]thiophene 4.31. The meto-branched phenylene units helped to form the macrocycle and reduced strain energy, but interrupted the overall conjugation. The synthesis of a corresponding pyridine-containing macrocycle 4.56 was attempted, but the ring-closure reactions of penta- and heptacyclic precursors failed [424]. 

Various synthetic approaches have been demonstrated for the synthesis of PAEs since early days [35 0], PAEs were synthesized by Ullmann condensation between bisphenols and aryl fcis-halide monomers using Cu(I) salt/pyridine as catalyst [36], General Electric developed the first commercially successful PAE poly(2,6-dimethyl phenylene oxide) (PPO) [38], It was prepared by oxidative coupling of 2,6-dimethyI phenol. However, this process has its own restrictions, because it does not allow much structural variation or inclusion of any electron-withdrawing group into the polymer main chain. First attempts to synthesize polysulfones (PSF) were successfully done by Friedel-Crafts sulfonylation reaction of arylenedisulfonyl chlorides, for example, diphenyl ether-4,4 -disulfonyl chloride with diaryl ethers, for example, diphenyl ether, or by self-condensation of 4-phenoxy benzene sulfonyl chloride in the presence of FeCls [41], Whereas the former reaction involves side reactions (sulfonylation not only in the para- but also in the ort/io-position), the latter produces only the desired linear all-para products. 

The activity of H. A. Staab with collaborators, which led to the definitely successful synthesis of cyclo[d.e.d.e.d.6.d.e.d.e.d.e]dodecakisbenzene (kekulene), went on parallel with the attempts of W. Jenny and collaborators described above. It is noted (Vogtle and Staab 1968) that the unambiguous nomenclature for cycloarenes was chosen according to an advice from "Beilstein—Institut, Frankfurt/Main". The macrocyclic compound hexa-TTir-phenylene... 

The adaptation of these electrochemical reactions to the synthesis of PPP has mainly used Ni complexes. First attempts were reported by Schiavon et al. [158] but their material was not pure and contained a high proportion of nickel centres. Fauvarque et al. [159], however, reported the electroreductive synthesis of an almost nickel-ffee poIy(/ -phenylene). A typical procedure requires completely dry conditions, uses NiX2L2 [X = C1 or Br, L = P(Ph)3 or L2 = (Ph)2PCH2-CH2P(Ph)2] as the starting complex and consists of reducing it electrochemically to a zero-valent species in the presence of dibromobenzene or dibromobiphenyl according to Scheme 6,37 [160] ... 

The Ullmann reaction (Fig. 7) was also attempted for the synthesis of poly(p-phenylene), but onfy low-molecular-weight products with structural irregularities were obtained. The Ullmann reaction, however, was found suitable for the polymerization of substituted phenylenes such as methyl-, nitro-, and perfluoropheny-lene [244-247]. 

U+2-Cycloaddit ion React ions ° The idea that the Diels-Alder addition possibly could be usefxil as a polymer-forming reaction was carried over from Illinois where one of Marvel s students had attempted to make a bisbutadiene in which the diene units were connected by a phenylene unit. Some work with cyclopentadiene which we had started convinced me that polymerization via a Diels-Alder reaction might be possible with a biscyclopentadiene monomer. Although only low molecular weight polymers were obtained, this marked the beginning of research on the synthesis of aromatic polymers by cycloaddition reactions. 

The synthesis of anti-doublebent [5]phenylene 56 [74] commenced with the tet-rahalogenated C2h-symmetric 53 [75]. Another use of the versatile building block 23 provided 54. Subsequent coupling with TMSA and deprotection afforded 55. The cyclization initially failed when attempted with [CpCo(CO)2] as the catalyst, but was later rendered successful by the application of the milder [CpCo(eth)2] conditions [74]. 

---