Wydział Chemii

Natasza Sprutta

Lechosław Latos-Grażyński

2001

Chemistry-A European Journal

7

5099-5112

10.1002/1521-3765(20011203)7:23<5099::AID-CHEM5099>3.0.CO;2-M

Naukowa

Angielski

Artykuł

The acid-catalyzed condensation of pyrrole and 2,5-bis(p-tolylhydroxymethyl)thiophene yields two novel giant heteroporphyrins: 5,10,15,20,25,30,35,40-octa(p-tolyl)-41,43,45,47-tetrathia[36]octaphyrin(1.1.1.1.1.1.1.1) (S₄OP) and 5,10,15,20,25,30,35,40-octa(p-tolyl)-dihydro-41,43,45,47-tetrathia[38]octaphyrin(1.1.1.1.1.1.1.1) (S₄OPH₂). These tetrathiaoctaphyrins are interconvertible through dihydrogenation or dehydrogenation processes. Both compounds possess helical figure-eight geometry with two thiophene rings for S₄OP or two pyrrole rings for S₄OPH₂ in the ribbon-crossing center as shown by NOESY experiments. The synthesis of the figure-eight tetrathiaoctaphyrin implies a prearrangement process to form helical M or P dithiatetrapyrromethanes. The P–P or M–M condensation leads to the figure-eight molecule in competition with an intramolecular ring closure. Two dithiaporphyrin-like pockets of S₄OP or S₄OPH₂ behave as independent proton acceptors. The stepwise process yields symmetric or asymmetric cationic species that depends on whether an even or odd number of NH protons are added. Dihydrotetrathiaoctaphyrin contains 38 π electrons in its conjugation pathway, which corresponds to the formal [4 n+2] Hückel type π-electron formulation that is consistent with a modest diatropic ring current effect in their ¹H NMR spectra. The formal 4 n type π-electron formulation for tetrathiaoctaphyrin accounts for the residual paratropic shifts. A figure-eight conveyor-belt-like movement of the whole macrocyclic ring without a racemization step is proposed to account for the dynamic properties of S₄OP. The molecule shuttles between two degenerate configurations. A S₄OP–S₄OPH₂ couple may be considered as a molecular element which, while preserving the overall figure-eight geometry, “chooses” pyrrole or thiophene rings as spacers as a function of the macrocyclic oxidation state.

https://doi.org/10.1002/1521-3765(20011203)7:23<5099::AID-CHEM5099>3.0.CO;2-M

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