Double Ring Expansion from an Aromatic [18]Porphyrin(1.1.1.1) to an Antiaromatic [20]Porphyrin(2.1.2.1)

Abstract

Double ring expansion from a 5,15-diarylporphyrin to a 5,16-diaryl-10,11,21,22-tetradehydro[20]porphyrin(2.1.2.1) occurred through a reaction sequence consisting of oxidation with PbO2 to 5,15-dioxoporphodimethene, a Corey-Fuchs reaction with tetrabromomethane in the presence of triphenylphosphine, and Fritsch-Buttenberg-Wiechell rearrangement triggered by tert-butyllithium. The obtained tetradehydro[20]porphyrin(2.1.2.1) and its mono- and dihydrogenated congeners exhibited 20 π antiaromatic character, whereas overhydrogenated congeners bearing a saturated bridge were nonaromatic owing to disrupted π conjugation.

Sensitized Photochemical CO2 Reduction by Hetero‐Pacman Compounds Linking a ReI Tricarbonyl with a Porphyrin Unit

“…We tentatively assign the first reduction event to be ligand‐centered, and by considering the potentials of the reference compounds, we assume that the first reduction of Re‐TXP‐Zn would be at the terpyridine unit, whereas it most likely is situated at the porphyrin unit in case of Re‐TXP‐H 2 . Notably, for Re‐bpy and Re‐tpy the first reduction is centered at the bipyridine or terpyridine ligand, respectively . Accordingly, the second reduction event in Re‐TXP‐H 2 is most likely based on the terpyridine unit.…”

“…Notably, for Re-bpy and Re-tpy the first reduction is centered at the bipyridine or terpyridine ligand, respectively. [26] Accordingly,t he second reduction event in Re-TXP-H 2 is most likely based on the terpyridine unit. However,i nt he case of the Re-TXP-Zn complex, the irreversible reduction at apeak potential of À2.15 Vm ay either be based on the porphyrin unit or, alternately,o nt he Re I /Re 0 couple by comparison to Re-bpy, which shows an irreversible reduction peak at À2.10 V. [30] In summary,b oth metal-coordination fragments have an oticeable influence on the redox properties of the investigated hetero-Pacman compounds.…”

Synthesis of [14]Oxatriphyrins(2.1.1) and Their Transformation into Ethane‐Bridged Oxatripyrrins by Boron Complexation

“…Compounds 4·PF 6 and 5·PF 6 exhibit porphyrin-like Soret and Q-bands, reflecting their 14π-electron aromatic nature. [39][40][41][42][43][44][45][46][47] However, to date, anti-aromatic ring-contracted porphyrins have scarcely been reported. Compounds 4·PF 6 and 5·PF 6 show fluorescence at 578 nm (fluorescence quantum yield, Φ f = 2.6 % and fluorescence life time, τ f = 1.1 ns) and 616 nm (Φ f = 9.0 %, τ f = 2.3 ns), respectively.…”

Boron(III) Carbazosubphthalocyanines: Core‐Expanded Antiaromatic Boron(III) Subphthalocyanine Analogues

“…All these signals were slightly upfield-shifted when compared with those for carbazoles and phthalocyanines,a nd could be attributed to the paratropic ring current arising from the antiaromatic core of these compounds.T he effect, however,w as not as large as that of the previously reported porphyrinoids based on the degree of upfield shift. [5][6][7][8] Ther elatively large upfield shift for the two isoindole protons singlets for 3a, 3c,and 3d could be due to the additional anisotropic shielding effect by the neighboring aryl rings.…”

“…[1] Apart from their intrinsic interest from at heoretical point of view,t hese compounds exhibit intriguing optical and electronic properties.T hey can serve as potential electrode-active materials in rechargeable batteries [2] and ambipolar semiconductors for field-effect transistors. [3] To date,an umber of antiaromatic porphyrins [4] and their ring-expanded, [5] ring-contracted (e.g.norcorroles [6] and tetrahydronorcorroles [7] ), and core-modified (e.g.i sophlorins, [1c,8] oxatriphyrins, [9] and phenanthriporphyrin [10] ) analogues have been reported. Thea romaticity of these systems can be modulated through changing the physical and chemical environments,and by photoswitching the electronic states.…”