Electrochemistry of Methylated N‐Confused Free‐Base Tetraarylporphyrins in Nonaqueous Media

Abstract

Four methylated N‐confused free‐base tetraarylporphyrins, which are represented as N‐CH3(Ar)4NcpH2 (Ar =CH3OPh, CH3Ph, Ph or ClPh), were synthesized and characterized in terms of their spectral and electrochemical properties in nonaqueous media. The first one‐electron oxidation of each porphyrin is reversible and located at E1/2=0.51–0.71 V, whereas the first one‐electron reduction is quasi‐reversible and located between −0.98 and −1.11 V vs. SCE. The electrochemically measured HOMO−LUMO gap ranged from 1.62 to 1.73 V, depending upon the solvent and meso‐substituents on the macrocycle, and this range of values is similar to the HOMO−LUMO gaps of both the non‐methylated N‐confused porphyrins, (Ar)4NcpH2 (1.60–1.68 V), and the nitrated N‐confused porphyrins, NO2(Ar)4NcpH2 (1.58–1.68 V). The effect of the N‐methyl group on UV/Vis spectra and reduction/oxidation potentials as well as the mechanisms of electron transfer are discussed, and comparisons made with data in the literature for both the non‐methylated N‐confused porphyrins and related N‐confused porphyrins having the same meso‐substituents and an inner nitro‐substituted carbon atom.

Synthesis of Vanadyl Complexes of N-Confused Porphyrins and Their Bromoperoxidase-like Catalytic Activity

“…Figures and S11 (in the SI) represent the comparative cyclic voltammograms of all of the synthesized compounds. These vanadium NCPs showed two irreversible reductions in the range of −0.71 to −1.52 V. However, irreversible multioxidations in the range of 0.77–1.41 V are observed possibly due to the formation of rearranged or decomposed porphyrin radical anionic or cationic species. − In general, the addition of electron-withdrawing substituents makes an easier reduction and harder oxidation, whereas the reverse trend is observed for electron-donating substituents on porphyrins and corroles . A similar pattern was identified in the case of synthesized NCPs ( V-1 and V-2 ) (Figure ).…”

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

“…The first chemical functionalization of NCP was reported in 1995, where NCP was methylated with CH 3 I to give 2-Me-NCP 91 (Scheme ). , Further methylation proceeded at the inner nitrogen atom in the presence of Na 2 CO 3 , affording N , N ′-dimethylated NCP salts 92 – 94 in 82–92% yields as a mixture of isomers . Among three possible isomers, only 92 was isolated by crystallization as a major product.…”