Fused Aromatic and Antiaromatic Smaragdyrin Dimers.

Singly-linked aromatic [22]smaragdyrin BF2 complex dimer was synthesized by the reductive coupling of 16-brominated [22]smaragdyrin BF2 complex, which was oxidized to a stable diradical with PbO2. As the first example of fused smaragdyrin dimer, a fused [22]smaragdyrin BF2 complex dimer was synthesized by the oxidation of a CuCl-BF2 complex dimer with FeCl3 and subsequent reduction with NaBH4. After removal of the BF2 group, the singly-linked and fused aromatic dimers were oxidized to the corresponding antiaromatic [20]smaragdyrin free base dimers. The first oxidation and reduction potentials of these dimers are split depending upon the intramolecular electronic interactions, which are larger for the fused dimers. Despite the large electronic interactions, the aromatic and antiaromatic characters are well preserved in the fused dimers.

[22]Pentaphyrins(2.0.1.1.0) Displaying N-Fusion, Pyrrole-Rearrangement, and Dimerization Reactions Upon Oxidation and Metalation.

Exploration of expanded porphyrins with unprecedented reactivities has remained important. Here [22]pentaphyrins(2.0.1.1.0) were synthesized as a constitutional isomer of sapphyrin by acid-catalyzed cyclization of 1,14-dibromo-5,10-diaryltripyrrin with 1,2-di(pyrro-2-ly)ethenes. These pentaphyrins display roughly planar structures and varying aromaticities depending upon the vinylene structures. The 19,20-ditolyl pentaphyrin gave an N-fused product and an unprecedented pyrrole-rearranged product, depending upon the oxidation conditions. Remarkably, upon the metalation with CuCl, the N-fused product and the pyrrole-rearranged product afforded an inner b-b coupled face-to-face CuII complex dimer and an outer b-b coupled lateral CuII complex dimer, respectively, in fairly good yields. Further, [22]pentaphyrin(2.0.1.1.0) fused with a NiII porphyrin was effectively dimerized upon oxidation with MnO2 to give a 16-16' directly linked dl-dimer.

Carbazole Based Smaragdyrins: Synthesis, Aromaticity Switching, and Formation of a Spiro-Dimer.

Carbazole-incorporated smaragdyrin BF2-complex 3 was synthesized by SNAr reaction of 3,5-dibromo-8-mesityl-BODIPY 1 with 3,6-di(tert-butyl)-1,8-di(pyrrol-2-yl)carbazole 2 as a nucleophile. Demetalation of 3 with ZrCl4 gave the corresponding smaragdyrin free base 4 in a good yield. Oxidations of 3 and 4 with MnO2 gave smaragdyrins 5 and 6, respectively, both followed by aromaticity switching, since the oxidized products showed a moderate paratropic ring current owing to their 20π-electronic circuits. Further, treatment of 4 with [RhCl(CO)2]2 in the presence of NaOAc gave RhI complex 7, and oxidation of 3 with RuCl3 in the presence of triethylamine led to the formation of a spiro dimer product, 8.

BIII-Subporphyrins Bearing Distorted Metal-Coordinating Straps: CuII-Assisted meso-Fabrications.

BIII-subporphyrins 4, 5, and 6 possessing metal-coordinating carbaporphyrin-like pockets were synthesized by Suzuki-Miyaura coupling reactions. Compounds 4 and 5 gave PdII complexes 4-Pd and 5-Pd upon metalation with Pd(OAc)2 but did not give either their NiII or CuII complexes. Conversely, 6 was expected to induce distorted square planar coordination because of its 2,5-di(pyrid-2-yl)pyrrole strap. Indeed reaction of 6 with Cu(OAc)2 did not give its CuII complex but produced meso-alkoxy and meso-phenoxy products in the presence of alcohols and phenol, possibly via CuII-mediated C-H bond functionalization, which was further extended to meso-C-C bond-forming fabrications by using organoboronic acids. These CuII-mediated C-H bond meso-fabrications are the first example for porphyrinoid substrates.

Copper(II) Carbaporphyrins: Oxygenation Reactivities Dependent upon Coordinating Structures.

CuII metalations of carbaporphyrins 1-4 gave the corresponding CuII complexes 1-Cu, 2-Cu, 3-Cu, and 4-Cu with varying degrees of distortions in CuII square-planar coordination. Upon treatment with Cu(OAc)2, 1-Cu was inert but 2-Cu and 3-Cu gave the respective O-atom-inserted complexes 2-OCu and 3-OCu. Further, 3-Cu and 4-Cu were converted to meso-methoxynickel(II) porphyrins 3-OMe and 4-OMe, respectively, via treatment with Cu(OAc)2 in methanol. meso-Hydroxynickel(II) porphyrin 3-OH was obtained by the treatment of 3-OCu by acetic acid. The treatment of 4-Cu with Cu(OAc)2 in the presence of acetic acid gave 5,15-diketoporphyrinogen 4-O. CuII complexes of carbaporphyrins became more reactive with an increased distortion in CuII square-planar coordination.

Di(p-dibenzi)[40]decaphyrin(1.0.0.0.0.1.0.0.0.0) PdII Complex: A Weakly Hückel 38π-Aromatic Macrocycle.

Di(p-benzi)[40]decaphyrin(1.0.0.0.0.1.0.0.0.0) BF2 complex and tris(p-benzi)[60]pentadecaphyrin(1.0.0.0.0.1.0.0.0.0.1.0.0.0.0) BF2 complex were synthesized by Suzuki-Miyaura coupling of α,α'-diborylated tetrapyrrole BF2 -complex with 1,4-diiodobenzene. Bis-BF2 complex was converted to bis-PdII complex via its free base. Macrocycles bis-BF2 and tris-BF2 complex take Möbius topology but are nonaromatic, since the macrocyclic conjugation is disrupted by the locally aromatic 1,4-phenylene units. In contrast, bis-PdII complex is a weakly Hückel 38π-aromatic macrocycle as evinced by its red-shifted, enhanced, and structured Q-like bands and a small electrochemical HOMO-LUMO gap. Interestingly, one 1,4-pheylene part of bis-PdII complex takes a quinonoidal distorted structure and the other takes a usual benzene structure in a figure-eight conformation with Hückel topology.

Synthesis of Pyrrole-Sharing Fused Porphyrinoid Hybrids by Post-fabrication of Ni(II) Porphyrins.

Pyrrole-sharing fused hybrids of NiII porphyrin with PdII N-confused(NC)-corrole and PdII NC-oxaporphyrin were synthesized by post-fabrication of NiII porphyrins. Specifically this consists of Friedel-Crafts type aromatic substitution reaction of meso-free NiII porphyrin with α,α'-dibromotripyrrin and Pd(OAc)2 assisted cyclization, and final heating to induce a Pd-C bond formation. NiII porphyrins fused with PdII NC-corrole and with PdII NC-oxaporphyrins show coplanar structures with a shared pyrrole unit. In these hybrids, the PdII NC-oxaporphyrin is aromatic and the PdII NC-corrole is moderately antiaromatic and these local electronic properties interact to influence the whole network.

Stable Antiaromatic [24]Hexaphyrin(1.1.0.0.1.0) and Its Metal Complexes.

5,10,23-Trimesityl-substituted [24]hexaphyrin(1.1.0.0.1.0) was synthesized as a stable antiaromatic molecule by base-catalyzed twofold SNAr reaction and was reduced to the corresponding [26]hexaphyrin, which was an unstable aromatic molecule because it easily oxidized to the [24]hexaphyrin. The [24]hexaphyrin served as a ligand to give the bis-PdII complex and tris-RhI complex with unique structures. The former complex has two square-planar-coordinated PdII ions bridged by an acetate anion and shows a strong paratropic ring current, while the latter complex has three RhI ions coordinated with two pyrrolic nitrogen atoms and two carbonyl groups, but one carbonyl group is shared with two RhI ions in a unique manner.

Synthesis of Naphthalene- and Phenanthrene-Fused Smaragdyrins and Their BF2 Complexes.

Naphthalene- and phenanthrene-fused [22]smaragdyrin BF2 -complexes were synthesized by 1) Suzuki-Miyaura coupling of ß-brominated [22]smaragdyrin BF2 complexes with 2-formylarylboronates, 2) Witting-type methoxymethylenation of the formyl group, and 3) methanesulfonic acid-catalyzed cyclization reaction. Subsequently these BF2 complexes were deboronized and oxidized to the corresponding antiaromatic [20]smaragdyrin free bases. The installed fused structures led to decrease of the aromatic characters of the [22]smaragdyrin BF2 complexes and the antiaromatic characters of the [20]smaragdyrin free bases.

Gated Photochromism of Dithienylethene-Embedded Expanded Calixphyrins.

Dithienylethene (DTE)-embedded expanded porphyrins were synthesized and confirmed to be photochemically inactive due to the lowest excited state of the expanded porphyrins. On the other hand, DTE-embedded expanded calixphyrins exhibited reversible photochromism upon UV-irradiation to form colored closed forms, which reverted to colorless open forms upon red-light irradiation. The closed forms were oxidized with DDQ or the air to lock the recorded information by converting to photochemically inactive expanded porphyrins. This was unlocked by reduction with NaBH4 to restore expanded calixphyrins with photochromism activity. These gated photochromic behaviors were demonstrated in PMMA (polymethyl methacrylate) film.

Doubly N-confused and ring-contracted [24]hexaphyrin Pd-complexes as stable antiaromatic N-confused expanded porphyrins.

As isomers of the regular porphyrins, N-confused porphyrins have attracted extensive attention of chemists because of their unique chemical structures, chemical reactivities, and physical properties, which result in their promising applications in the fields of catalytic chemistry, biochemistry and material science. Typically, N-confused porphyrins are synthesized via acid catalyzed condensation and following oxidation during which lactams are often formed as the byproducts. Here we report doubly N-confused and ring-contracted [24]hexaphyrin(1.1.0.1.1.0) mono- and bis-Pd-complexes as stable antiaromatic N-confused expanded porphyrins, which are synthesized through Pd-catalyzed Suzuki-Miyaura coupling of 1,14-dibromotripyrrin. These macrocycles show a paratropic ring currents, an ill-defined Soret band, a red-shifted weak absorption tail, and a small HOMO-LUMO gap. NBS bromination of the bis Pd-complex give its mono- and dibromides regioselectively, which are effectively used to synthesize a [24]hexaphyrin dimer and a NiII porphyrin-[24]hexaphyrin-NiII porphyrin triad, respectively.

Post-Installation of Fused Benzoheptagons at the Periphery of NiII Porphyrins: Helical Structures and Conformation-Adjustable Fullerenes Binding.

Fused-benzoheptagon-installed NiII porphyrins were synthesized by a protocol consisting of (2-formyl)arylation at the meso-position(s) of NiII porphyrins, conversion of formyl group to methoxyethene group by Wittig reaction, and final Bi(OTf)3 -catalyzed cyclization. The structures of these porphyrins have been revealed by X-ray analysis. Owing to the installed heptagon ring(s), these porphyrins show curved structures with conformational flexibility. Dimer has been shown to have a small activation barrier for inversion and to capture C60 and C70 with large association constants with adjustable conformational changes.

Rhodium-Catalyzed [5 + 2] Annulation of Pyrrole Appended BODIPYs: Access to Azepine-Fused BODIPYs.

Rhodium-catalyzed C-H/N-H [5 + 2] annulations of 8-(pyrrol-2-yl)-appended boron-complexed dipyrromethenes (BODIPYs) with internal alkynes have been established to afford a series of azepine-fused BODIPYs with good yields and excellent regioselectivity, in which the pyrrol-2-yl unit serves as the directing group as a rare example. A RhI intermediate was obtained to indicate a RhI/RhIII catalytic process involved in this reaction. Importantly, the [5 + 2] C-H annulation is demonstrated as a concise strategy to change the optical properties of BODIPY.

Heptagon/Octagon-Fused Diporphyrins or Spiro-Pentagon-Bridged Dichlorin from p-Terphenylene-Bridged Diporphyrin.

Intramolecular fusion reactions of a p-terphenylene-bridged NiII porphyrin dimer gave different products, depending upon reaction conditions. Oxidation with Fe(OTf)3 provided syn- and anti-doubly heptagon-fused NiII porphyrin dimers showing enlarged π-electronic networks, probably via a radical mechanism, while treatment with methanesulfonic acid provided a spiro-pentagon-bridged NiII chlorin dimer via acid-catalyzed Friedel-Crafts type cyclization. Further, a doubly octagon-fused NiII porphyrin dimer was synthesized via a sequence of double meso-formylation, reduction to corresponding diol, and BF3 -catalyzed cyclization.

A Quadruply Bridged Non-Offset Face-to-Face Porphyrin Dimer and Cross-Shaped Pentameric Porphyrin Tapes Based on 2,7,12,17-Tetrakis(pinacolatoboryl) NiII Porphyrin.

2,7,12,17-Tetrakis(pinacolatoboryl) NiII porphyrin 5 Ni was synthesized in 75 % yield by Ir-catalyzed borylation of porphine followed by NiII metalation and has been demonstrated to be a useful synthon, giving 2,7,12,17-tetraaryated NiII porphyrins 6 a-d, peripherally octaarylated NiII porphyrins 8 a-d, quadruply bridged face-to-face non-offset NiII -porphyrin dimer 12, and cross-shaped ß-meso singly linked porphyrin pentamers and nonamers. Oxidation of cross-shaped ß-meso singly linked porphyrin pentamers 14 Ni and 14 Zn gave fused pentameric tapes 15 Ni and 15 Zn. The structures of 12, 14 Zn, and 15 Ni have been revealed by X-ray diffraction analysis. Optical separation of 12 has been accomplished, showing a bisignate coupling pattern for exciton-coupled blue-shifted Soret band. Pentameric porphyrin tape 15 Zn exhibits a red-shifted absorption band at 1156 nm and seven reversible redox waves.

m-Benziporphyrin(1.1.0.0)s as a Rare Example of Ring-Contracted Carbaporphyrins with Metal-Coordination Ability: Distorted Coordination Structures and Small HOMO-LUMO Gaps.

m-Benziporphyrin(1.1.0.0) and m-pyreniporphyrin(1.1.0.0) were prepared as ring-contracted carbaporphyrins. While m-Benziporphyrin(1.1.0.0) was unstable, m-pyreniporphyrin(1.1.0.0) was fairly stable. Both of their PdII complexes showed distorted coordination structures with extremely short Pd-C bonds. As compared with the reported m-benziporphyrin PdII complexes, these PdII complexes showed considerably small HOMO-LUMO gaps, despite their smaller molecular size. PdII metalation of the m-pyreniporphyrin(1.1.0.0) dimer gave the corresponding PdII complex, which showed similar distorted coordination and a smaller HOMO-LUMO gap. Finally, PdII metalation of a pyrene-sharing formal p-benziporphyrin(1.1.1.1) dimer gave a nonaromatic PdII dimer, which rearranged to an aromatic PdII complex upon treatment with alumina.

Facile Formation of Stable Neutral Radicals and Cations from [22]Smaragdyrin BF2 Complexes.

meso-Trimesityl-substituted [20]smaragdyrin freebase was synthesized by p-toluenesulfonic acid catalyzed reaction of 5-mesityldipyrromethane and 2,14-dibromodipyrrin in an improved yield of 63 %. Unexpectedly, treatment of the [20]smaragdyrin freebase with BF3 ⋅ OEt2 and triethylamine (TEA) gave a stable radical species, in which the BF2 unit is coordinated at the tripyrrin site, probably by ready release of a hydrogen atom of a [22]smaragdyrin BF2 complex. Similar treatment of [22]smaragdyrin free base produced another [22]smaragdyrin BF2 complex, in which the BF2 unit is coordinated at the dipyrrin site. The tripyrrin site coordinated neutral radical was oxidized with AgSbF6 to give a stable antiaromatic cation; this was reduced with NaBH4 to its 22π congener, which was easily oxidized back to the neutral radical in the air and rearranged to thermodynamically stable dipyrrin site coordinated [22]smaragdyrin BF2 complex upon treatment with BF3 ⋅ OEt2 and TEA. Further, the dipyrrin site coordinated [22]smaragdyrin BF2 complex was similarly oxidized to a stable neutral radical and a stable cation in a stepwise manner. This work demonstrates a rare ability of smaragdyrin BF2 complexes to exist in multiple redox states, particularly forming a stable neutral radical by facile release of a hydrogen atom.

Synthesis of Subporphyrin Free Bases.

BIII subporphyrins are the legitimate ring-contracted porphyrins consisting of three pyrroles and three meso-carbons and their chemistry has been extensively developed since the first synthesis in 2006. However, subporphyrin free bases have never been synthesized, despite tremendous attempts to remove the BIII ion. Here we report that Suzuki-Miyaura coupling between α,α'-diborylated tripyrrane 1 and tetrabromide 5 gave subporphyrin free bases 6, 6 A, and free base dimer 7 in 6 %, 4 %, and 2 % yields as the first examples. Subporphyrin free bases exhibit curved bowl-like structures and distinct 14π-aromaticity. Steady-state and time-resolved spectroscopy revealed that the excited-state behaviors of the subporphyrin free bases are comparable with those of the corresponding BIII subporphyrins. Rotational relaxation processes in the excited states have been revealed, which enhance the electronic interactions with the meso-aryl substituents and between the two subporphyrins.

Efficient Synthesis of Multiply Seven-Membered-Ring Fused Porphyrins by Rhodium-Catalyzed [5+2] Annulation.

Rhodium-catalyzed reaction of meso-pyrrol-2-yl NiII porphyrins with internal alkynes proceeded smoothly to give singly, doubly, and quadruply seven-membered-ring fused NiII porphyrins as the first example of [5+2] annulation reaction for porphyrin substrates, where the meso-appended pyrrole unit serves as a directing group. These reactions are operationally quite simple and easy. A plausible reaction mechanism was proposed on the basis of the isolation of a key intermediate. The structures of the representative products have been revealed to be considerably bent owing to the implemented seven-membered rings. Doubly fused ZnII and NiII porphyrins possessing an unsubstituted meso-position were dimerized to meso-meso linked dimers by aerobic oxidation with Zn(OAc)2 ⋅2 H2 O and electrochemical oxidation, respectively. The optical and electrochemical highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps, as well as the aromatic characters of the fused porphyrins decrease as the fusion parts increases.