Formation and Isolation of a Four‐Electron‐Reduced Porphyrin Derivative by Reduction of a Stable 20π Isophlorin

Abstract

The two-electron reduction of a diprotonated dodecaphenylporphyrin derivative by Na S O gave a corresponding isophlorin (Iph) selectively. Formation of Iph was confirmed by spectroscopic measurements and the isolation of tetramethylated Iph. Further reduction of Iph proceeded to form an unprecedented four-electron-reduced porphyrin (IphH ), which was fully characterized by spectroscopic and X-ray crystallographic analysis. IphH , with a unique conformation, could be oxidized to reproduce the starting porphyrin, resulting in a proton-coupled four-electron reversible redox system.

Facile Redox‐Induced Aromatic–Antiaromatic Interconversion of a β‐Tetracyano‐21,23‐Dithiaporphyrin under Ambient Conditions

“…Similar results were also observed in [D 7 ]DMF (Figure S3 b). No signals assignable to the NH proton were observed within the range of those for analogous compounds (from 30 to 7 ppm, Figure S7) . This indicates that [ 2 ] 2− is not protonated in solution.…”

“…The spectrum exhibitedasharp singlet signal for the b protons at d = 4.99 ppm (Figure 3c), which were, compared to 1,c onsiderably upfield shifted. Comparison of the chemical shifts of selected isophlorins with antiaromatic [7-14, 17, 18] and nonaromatic [3][4][5][6] characters, other relevant antiaromatic porphyrinoids, [29][30][31] and quinoidal thiophene compounds [32,33] is summarized in Ta ble S16. The peak of [2] 2À is shifted downfield compared to those of the stronga ntiaromatic analogues (from 3toÀ1ppm), but shifted upfield compared to those of the distortedn onaromatica nalogues and quinoidal thiophene compounds (from 8t o6ppm).…”

“…One is the deformed isophlorin. Introducing a substituent on their periphery or the internal nitrogen atoms changes their 20 π antiaromaticity, thereby improving their stability …”

“…Introducing as ubstituent on their peripheryo rthe internal nitrogena toms changest heir 20 p antiaromaticity,therebyimproving their stability. [3][4][5][6] The second typeo fi sophlorins contain tetravalent elements, such as Si or Ge [7][8][9] or their respective analogues. [10][11][12][13] They complementi sophlorins in terms of their charge valance because isophlorinss erve as tetravalent ligands.…”

Synthesis and properties of redox‐switchable zinc complexes of 10,15,20‐triaryl‐15‐aza‐5‐oxaporphyrin

“…In general, two‐electron‐ and one‐electron‐reduced porphyrins (20π and 19π porphyrins, respectively) are extremely unstable under atmospheric conditions because of their high‐energy highest occupied molecular orbital (HOMO) and singly occupied molecular orbital (SOMO), respectively . Several approaches have been proposed to isolate 20π and 19π porphyrins in neutral forms, which basically rely on the concept of lowering the HOMO or SOMO energy levels . However, most of the reported neutral 20π and 19π porphyrins are highly distorted and/or still air‐sensitive.…”