Corroles programmed for regioselective cycloaddition chemistry — synthesis of a bisadduct with C₆₀-fullerene

Abstract

A symmetrical b,b′-tetrasulfoleno-corrole is described here as an excellent and selective precursor to highly reactive corrole-b,b′-dienes, opening a selective route to specific b,b′-functionalized corroles via cycloaddition chemistry. The b,b′-tetrasulfoleno-corrole was prepared by acid catalyzed condensation of tolylaldehyde and a b,b′-disulfoleno-dipyrromethane, which was obtained by standard procedures. Crystalline deep green b,b′-tetrasulfoleno-corrole was isolated in 8-10% yield. Thermolysis of the corrole at 140 °C and in presence of an excess of C 60 -fullerene gave a difullereno-corrole selectively (> 80% yield). The spectroscopic data indicated attachment of the two fullerene units at the "western," directly connected pyrrole rings. The tetrasulfoleno-corrole thus showed a remarkable preference for loss of sulphur dioxide and subsequent cycloaddition at the two "western" rings. In the difullereno-adduct, two sulfolene groups in the remaining "eastern" b,b″-disulfoleno-pyrroles still are available as "caged dienes" for further thermal diene formation, and attachment of additional groups via [4 + 2]-cycloaddition reactions.

A Dipyrrin Programmed for Covalent Loading with Fullerenes

“…Each of these latter methylene signals coupled to C-atomsw ith chemical shift values of 39.2 ppm and 38.3 ppm (as seen in HSQC-spectra), as is typical for pyrrole b-methylene groupsl inked to af ullerene( Ta ble S1 and Figure S5). [13] In contrast, the other two methylene signals (3.14 ppm and 4.10 ppm) correlated to carbonsa t5 5.5 ppm and 53.4 ppm in the HSQC spectra of 2,i ndicating their attachment to the remaining sulfolene unit ( Figure S5). The deduced location of methylene groups was confirmed in a 1 H, 1 H-ROESY spectrum.T here, the signals at 3.60 and 3.14 ppm showed correlations with H-atoms at the ortho-position of the mesophenylg roup and were assigned to H 2 C3 1 and H 2 C7 1 ,r espectively ( Figure 3).…”

“…The pyrrole a-H was shifted to 8.02 ppm (Figure 3a nd Ta ble S1 in the Supporting Information). In the 1 H, 13 C-HSQC spectrum of 3,t he two methylene group singlets at 3.60 ppm and 4.48 ppm of the correlated to carbon resonances at 38.6 and 40.0 ppm of the neighboring fullerenea ddend ( Figure S7), and,i na 1 H, 13 C-HMBC spectrum, to the typical quaternary carbono ft he fullerene moiety at 66.4 ppm ( Figure S8). These correlations secured the attachment of the two fullerene units in 3.T he shielding effect of the phenyl group at the dipyrrin meso-position assisted the assignment of the signal at 3.60 ppm to H 2 C3 1 and H 2 C7 1 .W hen the 1 HNMR data of 1, 2 and 3 are compared, the signals of the pyrrole NH and a-H's, of the protons of the methylene group next to fullerene and at the ortho-positiono ft he mesophenyls ubstituent shift to lower field, upon consecutive loading with the C 60 -fullerene, whereas the signal of the protoni n the para-position of the meso-phenyl group shifts to higher field (Figure 3a nd Figure S2).…”

“…[10b, 12] From tetra-(b,b'-sulfoleno)porphyrins four SO 2 units were readily extruded consecutively at 140 8C, generating an array of highly reactive porphyrin-dienes,w hich provided au nique basis for attaching various dienophiles. [12b, c] In contrast, the corresponding, less symmetric tetra-(b,b'-sulfoleno)corrole [13] liberated the dieneu nits quickly at the directly linked ('western')p yrroles (9 min at 140 8C) and allowed the regioselective loading of ac orrole with two C 60fullereneu nits at the "western" pyrroles.B roadly functioning paths to porphyrinoid conjugates with C 60 -fullerenes are very useful,a st hese furnish attractive components of photovoltaic and other materials. [14] As reported here, heating of the di-(b,b'-sulfoleno)-dipyrrin 1 [15] liberated SO 2 very readily (in contrast to the analogous b,b'-sulfolenopyrroles [11a, 16] ), providing am ilda nd efficient path for twofold [4+ +2]-cycloaddition of the dienophile C 60 .…”

Synthesis, spectroscopic and crystallographic analysis of the Zn-complex of a di(β,β′-sulfoleno)pyrrin: model for Zn-complexes of bilirubin and of phylloxanthobilins

“…Our synthetic route to di( β , β′ -sulfoleno)pyrrin 2 relied on the earlier made corresponding di( β , β′ -sulfoleno)pyrromethane ( 1 ), available, in turn, from condensation of 3,5-di- tert -butylbenzaldehyde and β , β′ -sulfolenopyrrole [ 13 ]. Dipyrromethane 1 was oxidized with dicyanodichlorobenzoquinone (DDQ) to furnish bright yellow 2 in 76 % yield, after crystallization in CH 2 Cl 2 / n -C 6 H 14 (see Scheme 1 ).…”

“…The sulfoleno-units of the dipyrrin 2 and of the bis(dipyrrinato) Zn-complex 3 are, furthermore, ‘programmed’ for introduction of covalent modifications at the pyrrole β -positions by [4+2]-cycloaddition reactions. As was recently developed with porphyrinoids, such as tetra-sulfolenoporphyrins [ 23 – 25 ] and a tetra-sulfolenocorrole [ 13 ], the dipyrrinato-units of 2 and 3 could, thus, also open up efficient access to further designed functionalized supramolecular assemblies.…”