A solution of 3a (0.9 g, 6.1 mmol) in toluene (40 mL) was treated at -50°C with 4 m L of a solution of tris(ethene)nickel in toluene (2.0 mmol Ni(C2H4)?; titer determined by reaction with P(OCH,), and 1,5-cyclooctadiene). The stirred mixture was allowed to warm to room temperature in 30 min and the solvent was then removed under vacuum. At 45OC/IO-' torr, light green 4a sublimed, which is colorless in thin layers (75 mg, 0.19 mmol, 12.5%). MS: m / z 403
Novel [26]porphyrinogen~ [~I 24-28 were conveniently prepared in few steps from the pyrrole building blocks 19-23. The selectivity of the cyclization is explained by a conformational helical effect due to steric congestion of the pyrrole psubstituents. The aromaticity of the [26]porphyrins[*I 30-33, obtained e y dehydrogenation of the porphyrinogens, is evi-dent from the 'H-NMR spectra displaying 25-ppm shift differences for the inner and outer protons of the porphyrins. These pigments belong to the most intensive chromophores known so far, showing VIS absorptions at 544-550 nm with lg E values up to 5.9. Present addresses: I+] Bayer AG, D-47829 Krefeld; I++] Boehringer Ingelheim KG, D-55216 Ingelheim; I+++] Solvay Deutschland GmbH, D-30173 Hannover. pared to the formation of [ 18lporphyrinogens. A computeraided inspection[l0] of three-dimensional conformations of P-substituted vinylogous tetrapyrroles revealed an increasing support of the helical conformation B (Scheme 2) with the size of the P-substituents. Scheme 1. Porphobilinogen (1) and the biomimetic transformation of its derivative 2 to [26]porphyrinogen 4 and [26]porphyrin 3 Et Et t CH2OH Et 2 Et E t a E t NCH, H , C N~ Br, Et a E t NCH, HSCN Et \@I / / / Et Et / \ \ Et E t Et Et E t 3 4 2 Bre t / / NCH, H, CN \ NCH, H, CN \ The pyrroles 10-13 (Scheme 3) were chosen as suitable precursors to investigate steric effects on the biomimetic synthesis of [26]porphyrinogens. Three of them were syn-Novel Porphyrinoids, 15 505 Scheme 5. Preparation of the pyrrole building blocks 20-23 and the transformation of 19-23 to the [26]porphyrinogens 24-28 12 10 13 11 KOH/DMSO, CH, I 1 7 5 z 187 % 176 % 180 Z CH, 19 20 21 22 23
The twofold vinylogously enlarged porphyrin with a 22-rcelectron system 3 was prepared by vinylogous bisformylation of the dipyrrylmethane 7 to give 8 and subsequent acid-catalyzed condensation of 8 with 7. The [22]porphyrin 3 is characterized by a Soret band at 469 nm, which on protonation of the porphyrinoid becomes very narrow with the highest extinction coefficient so far observed for an organic pigment (E = 1090000). In the 'H-NMR spectrum 3 reveals a strong diamagnetic ring-current effect with a shift difference between inner and outer protons of A6 = 20.1 ppm, thereby proving itself a pronounced aromatic system.
quenz-lmpedanzanalysator HP 4192A gemessen. In der imaginiiren Impedanzebene ergaben sich Halbkreise, die bis zum Nullpunkt extrapoliert werden konnten und von Geraden mit einem Winkel zu den Achsen von etwa 45" gefolgt wurden. Fur die Analyse konnte daher ein einfacher Debyescher Ersatzschaltkreis verwendet werden. Zur Kontrolle der ionischen Leitung wurden Gleichstrom-Polarisationsmessungen [ I l l in einem Spannungsbereich 0-1
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