Reorganization of the intramolecular hydrogen bonding network in 1,14-di(arylamino)-5,10-di(ethoxycarbonyl)-tripyrrins

Abstract

Recently we have reported that 1,14-diaminated tripyrrins form a double helical structure via interstrand hydrogen bonding interaction in non-polar solvents. In this work, ethoxycarbonyl-substituted 1,14-di(arylamino)tripyrrins were prepared by nucleophilic substitution reaction. The structure has been revealed by X-ray analysis to be a ([Formula: see text]-syn, [Formula: see text]-syn) conformer stabilized by intramolecular hydrogen bonding between the pyrrolic NH proton and the ester carbonyl oxygen atom. This conformer was likely formed as a meta-stable state in solution since thermal isomerization into a ([Formula: see text]-syn, [Formula: see text]-syn) conformer was observed in DMSO via NH tautomerization.

Double helices of dissymmetrical α,α′-disubstituted tripyrrins

“…α,α′-Dianilinotripyrrins have been shown to be in the monomeric form in DMSO due to the hydrogen bonding between the amine NH and DMSO. 6,11 Consistently, the 1 H NMR spectra of 2a and 2b in DMSO- d 6 exhibit signals corresponding to the monomeric form (Fig. S2-4 and S2-9; see the ESI†).…”

“…According to our previous report, 6,11 monosubstitution of α,α′-dibromotripyrrin 3 12 was effective by the addition of an equimolar amount of aniline in acetonitrile at room temperature. Here, we chose 3,5-bis(trifluoromethyl)aniline as a nucleophile because of the larger association constant of 1a .…”

Synthesis and Dynamic Behaviors of 5,7,8,10-Tetraphenyl-1,14-dianilinotripyrrins

“…1 Different from dipyrrins and porphyrins, the three pyrrolic nitrogen sites serve to have a weak intramolecular hydrogen-bonding network susceptible to the environments. 2,3 Without any substituents at the terminal pyrrolic -positions (i.e., 1,14-positions) that are reactive toward nucleophiles, tripyrrins are unstable in the solution state. Therefore, most of reports on isolable tripyrrins have been limited to the protonated salts, 4 metal complexes, [5][6][7][8][9][10][11] or tripyrrindione, an oxygenated derivative at the 1,14-positions.…”