Radikaldimerisierung von 5,5′-Diphenyl-3,3′,4,4′-tetramethoxy-2,2′-bipyrrol: π-Dimer im Kristall, σ-Dimer in Lösung

Merz, Andreas; Kronberger, Jürgen; Dunsch, Lothar; Neudeck, Andreas; Petr, Andreas; Pa̋rkányi, László

doi:10.1002/(sici)1521-3757(19990517)111:10<1533::aid-ange1533>3.0.co;2-w

Cited by 20 publications

(5 citation statements)

References 31 publications

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“…These findings and additional experimental results prove that the electropolymerization mechanism of chainlike conjugated polymers does not involve a chain propagation process with successive coupling steps of the starting radical cation . However, it must be concluded that the oligomerization in solution preferably occurs via consecutive “dimerization” steps leading from a dimer to a tetramer and then to an octamer (Scheme ). − Additionally, in all cases where the reaction rates between different reactive oligomers and the starting monomer are similar, trimers and pentamers may be formed within the initial period of oligomerization as well. The reactivities of the generated oligomeric intermediates depend on their respective charging level.…”

Section: Introductionmentioning

confidence: 74%

“…Therefore, a correlation between the number of pyrrole units N in a chain and the position of the absorbance maximum of a charged species is not posssible. However, it should be noted that the PPy chains during charging (oxidation) form “σ-dimers” which, in the case of α-coupling, double the chain length of the oligomer; − β-coupling cannot be excluded either . Nevertheless, the conjugation length remains in the same range and leads to broader bands or shoulders.…”

Section: Resultsmentioning

confidence: 99%

“…A further important point in understanding the formation and structure of conducting polymers concerns the existence and stability of charged σ-intermediates (Scheme ). These intermediates are formed within each coupling step during polymerization. − Experimental results as well as theoretical considerations clearly show that the stability of these σ-intermediates increases as a function of chain length and the proton elimination leading back to a neutral chain becomes slower and slower …”

Section: Introductionmentioning

confidence: 98%

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Relationship between Chain Length, Disorder, and Resistivity in Polypyrrole Films

Bufon¹,

Vollmer²,

Heinzel³

et al. 2005

J. Phys. Chem. B

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The effects of the polymerization temperature and of voltammetric cycling on the chain length and the resistivity of polypyrrole films are investigated. The studies provide further proof for the existence of at least two different types of polypyrrole, the so-called PPy I and PPy II. As the electropolymerization of conjugated systems in contrast to normal polymerization reactions is a fully activated process, the generation of these different types of PPy depends on experimental parameters such as temperature or formation potentials. UV-vis measurements demonstrate that PPy II comprises significantly shorter chains than PPy I (8-12 vs 32-64 units); moreover, film conductivity is found to increase with the fraction of PPy II. This fraction is changed via the polymerization temperature as well as by cyclic voltammetry, both of which can induce a metal-insulator transition. The counter-intuitive relationship between resistivity and chain length is interpreted in terms of disorder-dominated transport, in which the shorter chains of PPy II support the formation of delocalized electronic states, thereby increasing the localization length. Thus, our results are in agreement with recent broadband reflectivity measurements.

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Section: Introductionmentioning

confidence: 74%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

See 1 more Smart Citation

Relationship between Chain Length, Disorder, and Resistivity in Polypyrrole Films

Bufon¹,

Vollmer²,

Heinzel³

et al. 2005

J. Phys. Chem. B

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“…6b), where at 260 K the characteristic free cation radical bands decrease with increasing absorption of the dimers. Considering the semi-empirical PM3 calculations 7 and the preferable formation of sigma-dimers of small aromatic cations in solution 23 we attribute this dimer to the sigma-dimer (Th 2 ) 2+ .…”

Section: Resultsmentioning

confidence: 97%

Dimerization of thianthrene radical cations as studied by in situ ESR and UV-Vis-NIR voltammetry at different temperatures

Rapta

Kress

Hapiot

et al. 2002

Phys. Chem. Chem. Phys.

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“…3 In addition, certain electron-rich pyrrole derivatives are of interest because of their redox behaviour and their ability to provide polypyrroles. 4 Lithiated methoxyallene 2 is an extremely valuable building block for the synthesis of oxygen and nitrogen heterocycles. 5 With carbonyl compounds it provides furan derivatives after cyclization, 6 whereas its reaction with nitrones leads to 1,2-oxazines.…”

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confidence: 99%

An Expedient Synthesis of Pyrrole Derivatives by Reaction of Lithiated Methoxyallenes with Imines

Amombo¹,

Hausherr²,

Reißig³

1999

Synlett

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Addition of lithiated methoxyallene 2 to imines provided the expected allenyl amines in good yield. These could be cyclized with base or with silver nitrate to a variety of 2,5-dihydropyrrole derivatives. Selected examples describe their conversion to pyrrolidin-3-ones or 3-methoxypyrroles. Most importantly, this [3+2] cyclization method could also be applied to the synthesis of 2,5-disubstituted derivatives such as 26-28 and also to the preparation of the enantiopure compound 23.Syntheses of pyrrole derivatives are of great importance due to their presence in numerous biologically active compounds. 2 Therefore, many routes leading to this class of heterocycles have been developed. 3 In addition, certain electron-rich pyrrole derivatives are of interest because of their redox behaviour and their ability to provide polypyrroles. 4 Lithiated methoxyallene 2 is an extremely valuable building block for the synthesis of oxygen and nitrogen heterocycles. 5 With carbonyl compounds it provides furan derivatives after cyclization, 6 whereas its reaction with nitrones leads to 1,2-oxazines. 7 Surprisingly, no additions to simple imines have been reported, 8 which should furnish pyrrole derivatives. A recent publication describing reactions of 2 with SAMP-hydrazones providing enantiopure 3-methoxy-2,5-dihydropyrrole derivatives 9 prompts us to report our results with various imines. 10 Lithiated methoxyallene 2 was generated by the standard procedure employing n-butyllithium at -40°C, and after addition of N-tosylimine 1 11 followed by aqueous workup and purification the primary adduct 3 was obtained in 67% yield (Scheme 1). This intermediate could be hydrolyzed with acid to afford an a,ß-unsaturated ketone 10 or, more interestingly, converted into a-amino ester 4 by ozonolysis. 12In analogy to the behaviour of the carbonyl adducts 6 cyclization of 3 employing 0.15 equivalents of potassium tert-butoxide in DMSO furnished the desired pyrrole derivative 6 in 84% yield. Since an excess of base converts 6 into 5, the isomerization 3AE6 is better performed by using of 0.27 equivalents of silver nitrate in acetone 13 which gave a yield of 93%. 14 Cyclization of 3 and elimination of toluene sulfinate from intermediate 6 proceeded by use of 1.5 equivalents of KOtBu and furnished 3-methoxy-2-phenylpyrrole (5) in 71% yield. This compound was also formed by heating the primarily obtained lithium salt of 3 in DMSO. An obvious subsequent transformation of 2,5-dihydropyrrole derivative 6 is the hydrolysis of its enol ether moiety; treatment of 6 with 2N aqueous sulfuric acid provided pyrrolidinone 7 in 96% yield. Analogous experiments were successfully performed with N-tosyl imines derived from pivalaldehyde and cinnamyl aldehyde. Having established that highly reactive imines such as 1 behave similarly to carbonyl compounds, we studied less reactive N-aryl and N-alkyl imines. Scheme 2 presents selected examples of the additions of 2 to readily available imines 8, 10, 12, 15, and 17. Cyclization either with silver nitrate or under basic ...

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Radikaldimerisierung von 5,5′-Diphenyl-3,3′,4,4′-tetramethoxy-2,2′-bipyrrol: π-Dimer im Kristall, σ-Dimer in Lösung

Abstract: Das kristalline, spinlose π‐Dimer (1.+⋅PF6)2 erhält man bei der Oxidation des Bipyrrols 1 mit Ferroceniumhexafluorophosphat. Die elektrochemisch in Lösung nachgewiesene diamagnetische Spezies wurde NMR‐spektroskopisch als σ‐Dimer identifiziert.

Cited by 20 publications

References 31 publications

Relationship between Chain Length, Disorder, and Resistivity in Polypyrrole Films

Relationship between Chain Length, Disorder, and Resistivity in Polypyrrole Films

Dimerization of thianthrene radical cations as studied by in situ ESR and UV-Vis-NIR voltammetry at different temperatures

An Expedient Synthesis of Pyrrole Derivatives by Reaction of Lithiated Methoxyallenes with Imines

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