Synthesis of Three Asymmetric N-Confused Tetraarylporphyrins

Creation from Confusion and Fusion in the Porphyrin World─The Last Three Decades of N-Confused Porphyrinoid Chemistry

Confusion is a novel concept of isomerism in porphyrin chemistry, delivering a steady stream of new chemistry since the discovery of N-confused porphyrin, a porphyrin mutant, in 1994. These days, the number of confused porphyrinoids is increasing, and confusion and associated fusion are found in various fields such as supramolecular chemistry, materials chemistry, biological chemistry, and catalysts. In this review, the birth and growth of confused porphyrinoids in the last three decades are described.

Synthesis of N-Fused Dithia and Dibenzi Homoporphyrins

N-fused dithia and dibenzi homoporphyrins have been synthesized using [2+2] approach by condensing one equivalent of appropriate dithienyl/di p-phenylene ethene diol with one equivalent of N-confused dipyrromethane in CH2Cl2 under...

Large-Scale Green Synthesis of Porphyrins

A new methodology for porphyrin synthesis has been developed. This is a simple two-step protocol. The first step involves the condensation of pyrrole and aldehyde in an H2O-MeOH mixture using HCl. The obtained precipitate from the first step was dissolved in reagent-grade dimethylformamide (DMF) and refluxed for 1.5 h, followed by stirring overnight in the air at room temperature. Subsequent purification through column chromatography or crystallization resulted in the formation of pure porphyrins. Advantageously, this methodology does not need any expensive chemicals such as 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ), chloranil, and so forth as an oxidizing agent. This reaction also does not require a large volume of dry chlorinated solvents. Contrary to the reported methodologies, which are mostly ineffective in the gram-scale production of porphyrins, the present method perfectly caters to the need for gram-scale production of porphyrins. In essence, the current methodology does not represent the synthesis having the highest yield in the literature. However, it represents the easiest and cheapest synthesis of porphyrin on a large scale to obtain a reproducible yield of 10-40% with high purity. In a few of the examples, even column chromatography is not necessary. A simple crystallization technique will be sufficient to generate the desired porphyrins in good yields.

Attempted syntheses of N-confused hydroporphyrins through modified Lindsey routes

Unlike N-confused porphyrins which are well-known and extensively studied tetrapyrroles, N-confused hydroporphyrins are almost unknown, largely because so far they have resisted attempts at rational synthesis. Here, we report our efforts towards the total synthesis of N-confused hydroporphyrins. We have prepared N-confused building blocks analogous to the non-N-confused substrates in the Lindsey synthesis of sparsely substituted chlorins. We have systematically flipped the A, B and C pyrrole rings in the dipyrrolic precursors of the target N-confused macrocycles, preparing in total an N-confused “Western half” (tetrahydrodipyrrin) and two N-confused “Eastern halves” (brominated formyldipyrromethanes). These were subjected to a range of cyclization conditions. While we successfully isolated and identified three macrocyclic products, none of these proved to be the desired N-confused hydroporphyrin.

Zinc 2-N-methyl N-confused porphyrin: an efficient catalyst for the conversion of CO2 into cyclic carbonates

A zinc 2-N-methyl N-confused porphyrin (Zn(NCP)Cl) catalyst was developed for the solvent-free synthesis of cyclic carbonates from epoxides and CO₂.

Electrochemistry of N-confused inner amino-substituted free-base tetraarylporphyrins in nonaqueous media

Four N-confused free-base tetraarylporphyrins containing an amino group on the inner carbon of the inverted pyrrole were synthesized and characterized as to their electrochemical and spectroelectrochemical properties in dichloromethane and N,N-dimethylformamide containing 0.1 M tetra-[Formula: see text]-butylammonium perchlorate as supporting electrolyte. The examined compounds are represented as (NH[Formula: see text](Ar)[Formula: see text]NcpH[Formula: see text], where “Ncp” is the N-confused porphyrin macrocycle and Ar is a [Formula: see text]-CH[Formula: see text]OPh, [Formula: see text]-CH[Formula: see text]Ph, Ph or [Formula: see text]-ClPh substituent on each meso-position of the macrocycle. Each porphyrin undergoes multiple irreversible reductions and oxidations. The first one-electron addition and first one-electron abstraction are located on the porphyrin [Formula: see text]-ring system to give [Formula: see text]-anion and [Formula: see text]-cation radicals with a HOMO–LUMO gap ranging from 1.21 to 1.34 V in CH[Formula: see text]Cl[Formula: see text] and 1.06 to 1.12 V in DMF. Both electrogenerated products are unstable and undergo a rapid chemical reaction to give new electroactive species which can be further reduced at more negative potentials or further oxidized at more positive potentials. The effects of the inner amino-substituent on the UV-vis spectra and electrochemical properties of the porphyrin are discussed, and comparisons made to data in the literature for both structurally related N-confused porphyrins containing an inner carbon NO[Formula: see text] group and derivatives without the inner substituent.

Difunctionalized N-Confused Porphyrins: Synthesis, Fluorescence, and Electrochemical Studies

Seven di-substituted N-confused porphyrins (NCPs) 9–15 bearing two aryl functional groups (cis-A2B2 type) were synthesized in 4–7 % yields via [3+1] approach. The corresponding five 5,10-diaryl-substituted symmetrical tripyrranes 1–5 were prepared and condensed with 2,4-bis(hydroxypentaflurophenyl)pyrrole 6. Two outer N-methyl type A2B2 NCPs 14 and 15 were also prepared via a similar approach using a new key precursor 8. All the porphyrins 9–15 were characterized by high-resolution mass spectrometry, NMR, infrared spectroscopy, UV–visible spectroscopy, fluorescence spectroscopy, and cyclic voltammetry. Fluorescence studies of 9–15 showed blue-shifted emission maxima and lower Stokes shifts values when compared with N-confused tetraphenylporphyrin (NCTPP). Electrochemical studies indicated easier oxidation of N-methyl NCPs 14 and 15 when compared with remaining NCPs 9–13.