Figure-Eight Tetrathiaoctaphyrin and Dihydrotetrathiaoctaphyrin

Abstract

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 pi electrons in its conjugation pathway, which corresponds to the formal [4n + 2] Hückel type pi-electron formulation that is consistent with a modest diatropic ring current effect in their 1H NMR spectra. The formal 4n type pi-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.

Computational Studies on Optoelectronic and Nonlinear Properties of Octaphyrin Derivatives

“…They found that hydrogen bonding is effective for the development of Huckel antiaromatic expanded porphyrins. The molecular framework of octaphyrin is consistent with a 36 π-electron circuit within what can be considered a twisted double-side (orientable) Huckel topology (Sprutta and Latos-Grazyński, 2001; Flemming and Dolphin, 2002; Pushpan et al, 2002; Silva et al, 2002a,b; Hata et al, 2006). According to Osuka et al the hydrogens present near the crossing point of the octaphyrin resonate at δ = 17.14 and 8.60 ppm in the deshielding region.…”

“…The discovery of sapphyrins and expanded porphyrins have attracted the interest of researchers attributed to their diverse applications in materials science (Sprutta and Latos-Grazyński, 2001; Flemming and Dolphin, 2002; Pushpan et al, 2002; Silva et al, 2002a,b; Cavaleiro et al, 2003; Hata et al, 2006; Tanaka and Osuka, 2016). The defining feature of these macrocycles is the presence of a larger internal cavity as compared to those present in natural tetrapyrroles.…”

“…The defining feature of these macrocycles is the presence of a larger internal cavity as compared to those present in natural tetrapyrroles. More specifically, expanded porphyrins are macrocyclic compounds containing five-membered heterocyclic units (like pyrrole, furan, or thiophene) linked together, either directly or through spacers with internal ring pathway contains at least 17 atoms (Sprutta and Latos-Grazyński, 2001; Flemming and Dolphin, 2002; Pushpan et al, 2002; Silva et al, 2002a,b; Hata et al, 2006). Their distinctive physical and structural properties have found applications in nonlinear optical (NLO) materials (Marder et al, 1997; Zhou et al, 2002; Ahn et al, 2005; Rath et al, 2005a; Misra et al, 2006), photosensitizers for photodynamic therapy (PDT) (Harriman et al, 1989; Maiya et al, 1989), transition or rare earth metal ion chelates, cation and anion receptors (Shionoya et al, 1992; Jasat and Dolphin, 1997; Sessler et al, 2000a,b; Sessler and Davis, 2001; Chandrashekar and Venkatraman, 2003), magnetic resonance imaging (MRI) contrasting agents (Charrière et al, 1993; Weghorn et al, 1996; Werner et al, 1999) and a tool for accessing presently unknown higher aromatic systems (Sessler et al, 1993).…”

Engineering macrocyclic figure-eight motif

“…25 The condensation reaction of 2,5-bis(p-tolylhydroxymethyl) thiophene and pyrrole under acid catalysis yielded A and B in 2% yield (figure 11). Exposure of A to NaBH 4 in THF transformed to B.…”

Dynamic behavior and strategy for the complete 1H and 13C assignments for meso-aryl expanded heptaphyrins

“…Usually all expanded porphyrins show broad 1 H resonance signals at room temperature, which is difficult for further progression of study [16] in the molecule. The broadening in the NMR spectrum at normal temperature is due to rapid rotation of the heterocyclic rings and at low temperature the rate of rotation is reduced relative to the NMR timescale [17].…”