Figure-eight tetrathiaoctaphyrin and dihydrotetrathiaoctaphyrin

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)-di- hydro-41,43,45,47-tetrathia[3 8]octaphyrin(1.1.1.1.1.1.1.1)(S4OPH2). These tetrathiaoctaphyrins are inter convertible through dihydrogenation or dehydrogenation processes. Both comp ounds possess helical figure-eight geometry with two thiophene rings for S4 OP 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 dithiatetrapyrrome thanes. The P-P or M-M condensation leads to the figure-eight molecule in c ompetition with an intramolecular ring closure. Two dithiaporphyrin-like po ckets Of S4OP or S4OPH2, behave as independent proton acceptors. The stepwi se process yields symmetric or asymmetric cationic species that depends on whether an even or odd number of NH protons are added. Dihydrotetrathiaocta phyrin contains 38 pi electrons in its conjugation pathway, which correspon ds to the formal [4n + 2] Huckel type pi -electron formulation that is cons istent with a modest diatropic ring current effect in their H-1 NMR spectra . The formal 4n type a-electron formulation for tetrathiaoctaphyrin account s for the residual paratropic shifts. A figure-eight conveyor-belt-like mov ement of the whole macrocyclic ring without a racemization step is proposed to account for the dynamic properties Of S4OP. The molecule shuttles betwe en 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 thiophen e rings as spacers as a function of the macrocyclic oxidation state.