New porphyrinoids, 9. Synthesis of a bisvinylogous porphyrin with a [22] annulene system

Abstract

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.

Shaping a Porphyrinoid Frame by Heteroatoms Extrusion: Formation of an Expanded [22]Triphyrin(6.6.0)

“…The extreme downfield and upfield positions of the resonances of the outside and inside perimeter protons, respectively, confirm the aromaticity of this expanded porphyrinoid. The rough aromaticity measure Δ δ , defined as the greatest difference between chemical shifts of the outer and inner protons, equals 19.12 ppm, which is close to the Δ δ range of 20–23 ppm observed for planar [22]porphyrins . The signals broadening, visible in Figure A, is a result of dynamic equilibria in solution, where interactions with anions and water play an important role (see below).…”

“…The rough aromaticity measure Dd,d efined as the greatest differenceb etween chemical shifts of the outer and inner protons, equals 19.12 ppm, which is close to the Dd range of 20-23 ppm observed for planar [22]porphyrins. [50][51][52] The signals broadening, visible in Figure 2A,isaresult of dynamic equilibria in solution, where interactions with anions and water play an important role (see below).…”

Expanded Porphyrins and Their Heterologs

“…The UV−visible spectra of these macrocycles are all dominated by an intense Soret absorption at 463 nm ( 200 and 196a (Figure )), , and 469 nm ( 195 (Figure )), with, for example, additional bands at 498 (103 100), 597 (280 000), 723 (6 600) and 812 (2 700) for 195a (Figure ) . Upon protonation, to give 195b , the Soret band becomes extremely narrow and significantly more intense (ε = 1 090 000 M -1 cm -1 ) due to the increased symmetry of the molecule.…”

“…For their initial approach, they looked toward the time-honored MacDonald “2 + 2” methodology frequently employed in total syntheses of classic [18]porphyrins . Of the two possible pathways presented by this “2 + 2” strategy, they found the route employing dipyrromethanes as the precursors more productive than the alternative approach (which is analogous to Scheme ) utilizing the unstable dipyrrylpropenes (i.e., compounds analogous to 176 and 177 ) . Thus, as shown in Scheme , dipyrromethane 191 served as the common intermediate, which when treated with (dimethylamino)acrolein and POCl 3 at −20 °C provided the second half of the macrocycle, the vinylogous dialdehyde 193 .…”

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34 Electronic absorption spectra of 195a in CHCl 3 (- - -) and in CHCl 3 /1% TFA (); the visible region has been expanded for clarity. (Modified from ref . )

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