Scalable Synthesis and Supramolecular Assembly of trans‐A₂B₂ Porphyrins with Pendant Carboxylic Functional Groups

Abstract

This article deals with facile synthesis of A2B2 porphyrins bearing carboxylate groups at 5,15‐ positions and different functional groups at 10,20‐ positions viz. 4‐iodophenyl (a), 4‐tert‐butylphenyl (b), 3,5‐dimethoxyphenyl (c) 3‐carboxyphenyl (d), 2‐thienyl (e) 4‐nitrophenyl (f), 4‐methoxy‐2,3,5,6‐tetrafluorophenyl (g) and 2‐pyrenyl (h) as single major component in scalable yields. It relates also to the supramolecular assembly modes of these species. The use of stoichiometric amounts of trifluoroacetic acid in condensation of 5‐(4‐methoxycarbonylphenyl)dipyrromethane and different aldehydes led to the formation of trans‐porphyrins as di‐esters (1 a‐1 h). These were transformed by hydrolysis to the corresponding di‐acids (2 a‐2 h). (1 a‐1 h) and (2 a‐2 h) were then core‐metalated to afford the corresponding metalloporphyrin species (3 a‐3 h) and (4 a‐4 h). The absorption and emission spectra of the free base (2 a‐2 h) and metallated porphyrins (4 a‐4 h) were found greatly influenced by the substituents at 10,20‐positions. SEM studies of solids deposited on surfaces from solution exhibited hydrogen‐bonded block‐shaped structures of 2 e and fibrous sheets of 2 f. Co‐crystallization of 2 a and 2 g with 4,4′‐bipyridyl yielded hetero‐molecular structures stabilized by both hydrogen O−H⋅⋅⋅N, and halogen N⋅⋅⋅I bonds in 2 a, and by O−H⋅⋅⋅N hydrogen bonds and C−F⋅⋅⋅π interactions in 2 g.

Database Investigation of Halogen Bonding and Halogen···Halogen Interactions between Porphyrins: Emergence of Robust Supramolecular Motifs and Frameworks

“…In addition to a consideration of the I bonds to the overall π system of the carboxylate or carboxylic acid group. This is exemplified by structures with CSD codes LOHVOV 123 and IFEBUT 124 (Figure 14). I•••N Interactions.…”

“…In such systems, unusually small metal–O···I and C–O···I angles may be indicative of the uncommon formation of I···O halogen bonds to the overall π system of the carboxylate or carboxylic acid group. This is exemplified by structures with CSD codes LOHVOV and IFEBUT (Figure ).…”

Impact of Electron-Withdrawing Effect on Sigma Hole Via Bromine-Based Interactions in Zn-5,10,15,20-tetra(4-bromo-2,6-difluoro Phenyl) Porphyrin

“…A strong hydrogen bond also operates between the 2D supramolecular sheets though NA moieties coordinated to the Zn­(II) center of the porphyrin. A hydrogen bond is observed between the COOH groups of NA through a pair of O2–H2···O1 interactions with an H···O distance of 1.84 Å to form R 2 2 (8) synthons (Figure b) . As only one NA coordinates to the Zn­(II) center, hence the R 2 2 (8) dimer joins the adjacent 2D sheets to form a 3D framework.…”

Open MOFs with Unique Hexatopic Zinc-5,15-bis(4′-carboxyphenyl)-10,20-bis(3′,5′-dicarboxyphenyl)porphyrin Linker

“…To this end, we have synthesized the [(5,15-bis­(4′-carboxyphenyl)-10,20-bis­(3′,5′-dicarboxyphenyl)]­porphyrin (H 6 HCPP) ligand that is a kind of a linker in which the coordination characteristics are similar to the well-known tetra­(4-carboxy)­phenylporphyrin (H 4 TCPP) and the tetra­(3,5-dicarboxy)­phenyl porphyrin (H 8 OCPP) linkers. The preparation of the H 6 HCPP followed the principles of our previously reported scalable synthesis of A 2 B 2 -type porphyrins (carefully controlling the concentration of TFA) . Formulation of single-crystalline MMPFs with Zn-H 6 HCPP is elusive due to the multiple coordination ability of this ligand.…”

“…The preparation of the H 6 HCPP followed the principles of our previously reported scalable synthesis of A 2 B 2 -type porphyrins (carefully controlling the concentration of TFA). 22 Formulation of single-crystalline MMPFs with Zn-H 6 HCPP is elusive due to the multiple coordination ability of this ligand. Their successful synthesis was achieved following our recently reported ameliorated methodology, i.e., the use of NaOH as modulator in the reaction mixture.…”