Tetrabromo[36]octaphyrin: A Promising Precursor of Directly Fused Porphyrin(2.1.1.1) Dimer and meso‐α Fused N‐Confused Porphyrin Dimer

Abstract

3,7,23,27‐Tetrabromo[36]octaphyrin 2 was synthesized as a novel octaphyrin bearing two meso‐free positions. Surprisingly, its ZnII and NiII complexation reactions produced a directly fused porphyrin(2.1.1.1) dimer 6, and a meso‐α fused N‐confused porphyrin (NCP) dimer 7, as the first example of NCP tape, respectively, via transannular C−C bond formation. While 6 exhibits a diatropic ring‐current effect owing to the global 36π Möbius aromaticity, 7 shows a paratropic ring‐current effect due to the global Hückel 36π antiaromaticity. In addition, the oxidation of 7 with PbO2 allowed for formation of its two‐electron oxidized species 9 that exhibited a diatropic ring‐current effect due to the global Hückel 34π aromaticity. This work has demonstrated that meso‐free large expanded porphyrins can be a promising platform to produce novel fused porphyrinoids.

Synthesis of Directly‐Linked Porphyrin−Pyricorrole Hybrid via Rearrangement of Internally‐bridged Octaphyrin(1.1.1.1.1.1.1.1) Upon Ni(II) Metalation

“…Internally-bridged octaphyrin 1 was prepared from 5,10,15,25,30,35-hexakis(pentafluorophenyl)octaphyrin (i. e., meso-free octaphyrin) in two steps. [6,8] We initially envisioned that Ni II metalation of 1 may lead to meso-meso linked porphyrin dimer 2Ni. According to the DFT calculations, the formation of 2Ni is thermodynamically more favorable as compared with the case of 2Zn (See the Supporting Information, SI).…”

A Fully Conjugated Porphyrin‐[36]Octaphyrin‐Porphyrin Hybrid Tape Exhibiting Möbius Aromaticity

“…As shown in Scheme 1, we employed a [2 + 2 + 2 + 2]-type cross-condensation reaction for synthesis of octaphyrin bearing two Ni II porphyrins, which was used in our recent synthesis of tetrabromo[36]octaphyrin 13. [5] As our first attempt, acidcatalyzed cross-condensation of dipyrromethane dicarbinol 6 with meso-porphyrinyldipyrromethane 8 [4a] was examined under usual acid-catalyzed conditions. After oxidation, however, singly-linked porphyrin-[36]octaphyrin hybrid trimer 9 was not detected.…”

“…Then, we examined Zn II metalation of 10, since tetrabromooctaphyrin 13 underwent spontaneous transannular meso-meso bond formation upon Zn II metalation to give Möbius aromatic bis-Zn II tetrabromo[36]octaphyrin 14. [5] Indeed, metal- [36]octaphyrin segment takes on a twisted structure with a dihedral angle of 88.5(7)°with respect to the Ni II porphyrin (Figure 2). [9] Importantly, in the 1 H NMR spectrum, the signals due to the β-protons of the [36]octaphyrin segment are observed at 8.27, 7.47, 7.31, 7.13, and 6.97 ppm, indicating a clear diatropic ring current.…”

“…vs. Fc/Fc + in V, and electrochemical HOMO-LUMO gaps (ΔE) for 10-12, 14, 15, and 4Ni. [a] [5] 0.53 0.28 À 1.05 1.33 15 [4c] 0.58 À 1.83 2.41 4Ni [4c] 0.26 À 0.41 0.67…”

Synthesis of meso‐Free Decaphyrin(1.1.1.1.1.1.1.1.1.1) by a Hydrodebromination Protocol; Aromaticity and Solvent‐Polarity Dependent Conformational Change

“…Meanwhile, we found that 3,7,23,27-tetrabromo[36]octaphyrin was synthesized by using 3,7-dibromodipyrromethane dicarbinol 6 with dipyrromethane in the [2 + 2 + 2 + 2] manner with a quite suppressed formation of [2 + 2] product (i. e. 3,7-dibromoporphyrin). [11] Then, we aimed at the [2 + 3 + 2 + 3] type synthesis of tetrabromodecaphyrin by cross-condensation of tripyrrane 7 with dibromodipyrromethane dicarbinol 6 (Scheme 1). [12] After some screening, we found that p-toluenesulfonic Br 4 [M-H] À : 2422.8195), respectively.…”