Über zweistufige Redoxsysteme, XI¹⁾ Diquartärsalze der Bipyridyle und Dipyridyläthylene. Synthese und Polarographie

Abstract

Die teilweise neu synthetisierten Redoxsysterne 2oX, 2Box, 30, und 40, wcrden polarographisch untersucht. Wahrend in Wasser nur die ersten Reduktionsstufen Ox/Sem (=E2) eindeutig auftreten, sind in Dimethylformamid und Acetonitril erstmals auch die Stufen Sem/Red (=El) reversibel gernessen worden, sofern sich die Red-Form der Systeme ,,chinoid" formulieren 1aBt. Die Semichinonbildungskonstante K von 2 , 2 B und 4 (107-1010) sinkt bei Einschiebung einer Vinylengruppe zu 3 auf ca. 103 ab. Two-step Redox Systems, X I ' ) . -Diquaternary Salts of Bipyridyls and Dipyridylethylenes : Syntheses and PolarographyThe partly newly synthesized redox systems 2oX, 2Box, 3ox and 40, were studied bypolarography. In water only the first reduction steps Ox/Sern (=E2) can be observed. However, in dimethylformamide and acetonitrile the steps Sem/Red (=El) were observed for the first time as being reversible in so far as Red has a ,,quinonoid" structure. The semiquinone formation constant K of 2 , 2 B and 4 (IO7-10*0) drops to about 103 in 3 when a vinylene group is introduced between the pyridine rings. A. ZielsetzungDie Beschreibung zweistufiger Redoxsysteme mit mehr oder weniger stabilem Radikalkation4) durch die allgemeine Struktur 1 lal3t drei grundsatzliche Variationen zu5.6). Eine davon bezieht die Endgruppe in ein cyclisch-konjugiertes System ein, das auf der hochsten Oxidationsstufe (lox) aromatischen Zustand besitzt. Musterbeispiel sind die schon seit 19207) untersuchten Dipyridiniumsalze 2(4,4')0x, die ,,Viologene"*), deren Charakter als zweistufiges Redoxsystem mit stabilem, violettem Radikalkation *) Korrespondenz bitte an diesen Autor richten.

Aromaticity and sterics control whether a cationic olefin radical is resistant to disproportionation

“…[12][13][14] Very similar redox properties are found for olens derived from biscationic paraquat (methyl viologen, respectively; 1,1 0 -dimethyl-4,4 0 -bipyridinylidene) 4, the related ortho-derivative (1,1 0 -dimethyl-2,2 0bipyridinylidene) 5, the dimethylaminopyridine (DMAP) dimer 6, 15 as well as 4,4 0 -bipyrylene 7. [16][17][18][19][20] The aza-analogues of TTF, i.e. tetraaminoethylenes or enetetramines, originate from the formal dimerization of unsaturated-(NHC, 8), saturated-(saNHC, 9) or benzannulated-(benzNHC, 10) N-heterocyclic carbenes (NHCs).…”

“… 12–14 Very similar redox properties are found for olefins derived from biscationic paraquat (methyl viologen, respectively; 1,1′-dimethyl-4,4′-bipyridinylidene) 4 , the related ortho -derivative (1,1′-dimethyl-2,2′-bipyridinylidene) 5 , the dimethylaminopyridine (DMAP) dimer 6 , 15 as well as 4,4′-bipyrylene 7 . 16–20 …”

Migration and Trapping of Photoinjected Excess Electrons in Double-Stranded B-Form DNA But Not in Single-Stranded DNA

“…39 DNA nucleosides, predominantly dC and to a lesser extent dT, can be easily reduced by excess electrons. 12, 13 The dC and dT electron adducts, even in their protonated forms, have more negative redox potentials (E ) -1.09 V vs NHE, pH 8.4-8.8) 39 than methylviologen (E°) -0.44 V vs NHE) 40 and thus can easily reduce 41 MV 2+ . In principle, the trapping of excess electrons by dC and dT can affect the migration distance.…”

Synthesis and characterization of a photosensitive interface for hydrogen generation: Chemically modified p-type semiconducting silicon photocathodes

“…An important departure from the electrochemical behavior of N,N'-dimethyl-4,4'-bipyridinium (methyl viologen) in solution, (MV2+/+-)soin, is found for the (PQ2+/+-)su{f derived from I. The dimethyl system in solution shows an E°(MV2+/+-)s.n at -0.45 V vs. SCE in CH3CN solvent and at -0.69 V vs. SCE in H20 solvent (12). Compound I can also be dissolved (accompanied by hydrolysis) in H20 and CH3CN, and a similar shift in the solution potential is observed.…”